Up to 100,000 people may have died in the Haiti earthquake, the Pan American Health Organisation has said, as the UN launches an appeal for more than $550m (£337m) in aid. 
 
 "A variety of sources are estimating the numbers [at] between 50,000 and 100,000," said Jon Andrus of PAHO, the Americas arm of the World Health Organisation. 
 
 Barack Obama said the US would do everything it could to get the country back on its feet. "The scale of the devastation is extraordinary ... and the losses are heartbreaking," he said at the White House. 
 
 In Britain, the Disasters Emergency Committee has launched an appeal for aid. The British Red Cross said £1m was raised in the first 36 hours of its appeal. 
 
 Initial estimates spoke of 45,000 to 50,000 deaths, and the sharp rise comes as peacekeepers in Haiti warn that security has become an urgent priority amid fears of a breakdown in order. 
 
 UN troops patrolling the capital said there was rising anger that aid had not been distributed quickly. The Brazilian military advised that aid convoys should add security to guard against looting. 
 
 "Unfortunately they're slowly getting more angry and impatient," said David Wimhurst, spokesman for the Brazilian-led UN peacekeeping mission. 
 
 "I fear … we're all aware that the situation is getting more tense as the poorest people who need so much are waiting for deliveries. I think tempers might be frayed." 
 
 Fevil Dubien, an aid worker, said some people were almost fighting over the water that he handed out from a truck in a northern Port-au-Prince neighbourhood. 
 
 Security was the biggest problem, Delfin Antonio Rodriguez, the rescue commander from the neighbouring Dominican Republic, told the AFP news agency. "Yesterday they tried to hijack some of our trucks. Today we were barely able to work in some places because of that." 
 
 The UN World Food Programme partly retracted a statement that looters had raided one of its warehouses containing 15,000 tonnes of food aid. In the new statement it said 6,000 tonnes of food remained in the building. A spokesperson said looting was not unusual in disaster situations when people were without the most basic supplies such as water. 
 
 The UN said it would launch a flash appeal this afternoon in New York for $550m in aid. A flash appeal is a way of structuring a co-ordinated humanitarian response. The former US president Bill Clinton said he would try to model a disaster assistance fund along the same lines he and former president George Bush Sr pursued for victims of the Asian tsunami. Barack Obama has asked Clinton, a UN special envoy to Haiti, to work with George Bush, the previous president, on a fundraising effort. 
 
 Hundreds of US troops and an aircraft carrier arrived in Port-au-Prince, raising hope that the situation would improve in the coming hours. 
 
 "We have much more support on the way," said the US commander in the capital, Lieutenant General Ken Keen. "Our priority is getting relief out to the needy people, to mitigate the suffering that the Haitian people are experiencing right now." 
 
 The US aircraft carrier Carl Vinson arrived off Haiti's shores overnight with 19 helicopters. It started flights from its deck this morning. 
 
 The carrier has water purifying equipment and three surgical operating rooms, and can do medical evacuations as well as ferrying supplies and people to and from land. 
 
 The arrivals added to more than 300 military personnel who had already landed in Haiti. 
 
 The 82nd Airborne was sending another 800 troops and aiming for a full brigade of 3,500 on the ground by the end of the weekend. 
 
 Jan Egerland, a former UN humanitarian chief, said he expected the arrival of aid to speed up. "We are in a very classic development. Days three, four and five are the most frustrating. Everybody knows that the whole world is mobilising and everyone has heard the promises. But it takes time to reach the beneficiaries. The infrastructure has either gone or totally clogged up," he told the BBC. 
 
 He said the inability of the Haitian government to direct relief operations and the death of the head of the UN mission in the country meant the US was effectively in charge of the situation. 
 
 The small airport in Port-au-Prince has struggled to cope with the stream of aid flights. Some have been turned away and little of the aid that has landed has arrived in the most needy areas. 
 
 Bodies lay all around the hilly city, with people covering their mouths and noses with cloth to block out the smell. Corpses were piled on pickup trucks and delivered to the general hospital in Port-au-Prince, where the hospital director, Guy LaRoche, estimated there were 1,500 bodies piled outside the morgue. 
 
 More than 48 hours after the 7.0 magnitude earthquake struck, people clamoured for food and water and continued digging for relatives missing under the rubble. "We need food. The people are suffering. My neighbours and friends are suffering," said Sylvain Angerlotte, 22. "We don't have money. We don't have nothing to eat. We need pure water." 
 
 Aid workers warned that time was running out for the thousands still trapped in the rubble. One described his frustration at hearing the cries of trapped people but being unable to help them because of a lack of heavy machinery. 
 
 Rezene Tesfamariam, the Haiti director of charity Plan International, said people were using their bare hands or basic tools such as shovels and pick-axes to dig for their loved ones. 
 
 "There are people still alive underneath [rubble], you can hear them crying for help, but time is running out. It is beyond the means of individuals to reach them. They are trying to move concrete with their hands. What is desperately needed is proper machinery and equipment to lift the rubble." 
 
 Tesfamariam said vehicles and equipment were urgently needed to remove the tens of thousands of bodies. 
 
 "I have been travelling round the city to find where we can provide assistance and I see dead bodies lying in the street everywhere." ||||| The US military's takeover of emergency operations in Haiti has triggered a diplomatic row with countries and aid agencies furious at having flights redirected. 
 
 Brazil and France lodged an official ­protest with Washington after US military aircraft were given priority at Port-au-Prince's congested airport, forcing many non-US flights to divert to the Dominican Republic. 
 
 Brasilia warned it would not ­relinquish command of UN forces in Haiti, and Paris complained the airport had become a US "annexe", exposing a brewing power struggle amid the global relief effort. The Red Cross and Médecins Sans Frontières also complained about diverted flights. 
 
 The row prompted Haiti's president, René Préval, to call for calm. "This is an extremely difficult situation," he told AP. "We must keep our cool to co-ordinate and not throw accusations at each other." 
 
 The squabbling came amid signs that aid was reaching some of the hundreds of thousands of people in desperate need of water, food and medicine six days after a magnitude 7 earthquake levelled the capital, killing more than 100,000, according to Haitian authorities. 
 
 The UN was feeding 40,000 and hoped to increase that to 1 million within a fortnight, said the secretary general, Ban Ki-moon, as he arrived in Port-au-Prince yesterday. "I am here with a message of hope that help is on the way," he said, speaking outside the severely damaged national palace. He also acknowledged "that many people are frustrated and they are losing their patience." 
 
 Ban said he has three priorities in Haiti: saving as many lives as possible, stepping up humanitarian assistance and ensuring the co-ordination of aid coming into the country. "We should not waste even a single item, a dollar," he said. 
 
 The plight of 80 elderly people at a partially collapsed municipal hospice just a mile from the airport, now a huge aid hub, showed the desperate need. The body of a dead 70-year-old man rotted on a mattress, nearly indistinguishable from the exhausted, hungry and thirsty people around him. "Others won't live until tonight," an administrator, Jean Emmanuel, told the Associated Press. 
 
 The Haitian government has established 14 food distribution points and aid groups have opened five emergency health centres. Water-purification units – a priority to avert disease and dehydration – were arriving. 
 
 But with aftershocks jolting the ruins, bloated bodies in the street and severe shortages of water and food many survivors had had enough: an exodus trekked on foot out of the city to rural areas. 
 
 The security situation worsened, with some looters fighting with rocks and clubs for rice, clothing and other goods scavenged from debris. In places the embryonic aid machine did not even try to organise distribution. Aid workers tossed out food packets to crowds and US helicopters took off as soon as they offloaded supplies, prompting scrambles in which the fittest and strongest prevailed. 
 
 "They are not identifying the people who need the water. The sick and the old have no chance," Estime Pierre Deny, ­hoping to fill a plastic container with water amid a scrum of people, told Reuters. 
 
 Frustration over aid bottlenecks among donors became tinged by national rivalry as it became clear the US was taking ownership of the crisis. A vanguard of more than 1,000 US troops was on the ground and 12,000 were expected in the region by today, including marines aboard the aircraft carrier USS Carl Vinson which anchored offshore as a "floating airport". 
 
 The Haitian government, paralysed by the destruction of the presidential palace and ministries, signed a memorandum of understanding formally transferring control of Toussaint L'Ouverture airport to the US. Former president Bill Clinton said he will travel to Haiti today to meet with government officials and deliver much-needed emergency supplies. 
 
 The UN mission, which had a 9,000-strong peacekeeping force in Haiti before the quake, seemed too stunned by its own losses to take control. Its dead include its Tunisian head, Hédi Annabi, his Brazilian deputy, Luiz Carlos da Costa, and the acting police commissioner, Doug Coates, a Canadian. 
 
 Flights seeking permission to land continuously circle the airport, which is damaged and has only a single runway, rankling several governments and aid agencies. "There are 200 flights going in and out every day, which is an incredible amount for a country like Haiti," Jarry Emmanuel, air logistics officer for the UN's World Food Programme, told the New York Times. "But most flights are for the US military. Their priorities are to secure the country. Ours are to feed. We have got to get those priorities in sync." 
 
 France, which as the former ­colonial power expects a prominent role, ­protested when an emergency field hospital was turned back. The foreign minister, Bernard Kouchner, said the airport was not for the international community but "an annexe of Washington", according to France's ambassador to Haiti, Didier Le Bret. 
 
 Brazil, which saw its leadership of the UN peacekeeping mission as a calling card of its burgeoning influence, was also indignant when three flights were not allowed to land. The foreign ministry reportedly asked Hillary Clinton to grant Brazil priority over chartered flights. Nelson Jobim, the defence minister, said Brazil would not relinquish command duties and suggested it, not Washington, would continue to lead UN forces. Analysts said it was vital command issues be resolved. 
 
 The Red Cross and Médecins Sans Frontières complained about flights with medical staff and equipment which were redirected to the Dominican Republic. "We are all going crazy," said Nan Buzard, of the American Red Cross. 
 
 The Obama administration has enlisted former presidents George Bush and Bill Clinton to spearhead relief efforts. In a series of interviews both men deflected right-wing accusations that the White House was seeking political advantage from the disaster. "I'd say now is not the time to focus on politics," Bush said, as he sat beside his predecessor. "You've got children who've lost parents. People wondering where they're going to be able to drink water."
– Earthquake survivors desperate for food broke into a UN warehouse in Port-au-Prince today, a sign of the growing frustration at delays in relief. UN officials say they've recovered nearly all of their stocks, however, and pledged to hand out 6,000 tons of food shortly. But with necessities such as water, medical supplies, and heavy moving equipment slow to arrive, anger and despair are rising among the tens of thousands of survivors in the capital. "We're all aware that the situation is getting more tense as the poorest people who need so much are waiting for deliveries," a Brazilian peacekeeper tells the Guardian. "They are slowly getting more angry," a UN official tell the New York Times. In other developments: Cuba gave the US permission to use its airspace for relief flights. About 4,000 inmates who escaped from the main prison remain at large. About 7,000 bodies have been buried so far in a mass grave. Two big aftershocks rattled the capital again today.