Media playback is unsupported on your device Media caption Oceanographer Dr Simon Boxall: "If this is the pulse, this becomes a viable search" 
 
 A Chinese ship searching for the missing Malaysia Airlines plane in the southern Indian Ocean has picked up a pulse signal, Chinese media say. 
 
 They say the signal has a frequency of 37.5kHz - the same as those emitted by the flight recorders. 
 
 However there is no evidence so far that it is linked to MH370. 
 
 Dozens of ships and planes have joined the search, with the operation moving into its most intensive phase before batteries on the data recorders fade. 
 
 On Saturday the Haixun 01 - one of two Chinese ships in the area - picked up the signal at about 25 degrees south latitude and 101 degrees east longitude, the state-run Xinhua news agency said. 
 
 "It is yet to be established whether it is related to the missing jet," it cautioned. 
 
 Media playback is unsupported on your device Media caption Richard Westcott reports on the use of a pinger locator to find a black box 
 
 China's Liberation Daily reported that three people on board had heard the signals, which were not recorded as they came suddenly. 
 
 Image copyright Reuters Image caption Officials said there was "some hope" the locators would be able to find the black box 
 
 The head of the Australian agency co-ordinating the search said the reported signals "are consistent with the aircraft black box" but "there is no confirmation at this stage that the signals and the objects are related to the missing aircraft". 
 
 The flight is believed to have crashed in the southern Indian Ocean, although no confirmed debris has been found. 
 
 Analysis This could be potentially significant, but caution is necessary. There have been many apparently promising leads over the past few weeks that have looked like the search team closing in, only for those leads to turn into nothing. The tantalizing element is the frequency of the signal supposedly picked up. It is consistent with a black box pinger. But we know very little more about the nature of the contact. The Chinese ship is not among those that have been mentioned before as having special equipment to search for the black box pinger, but it is a very modern search-and-rescue vessel. Even with the sophisticated listening devices now being deployed in the search, the size of the search area, the range of the pinger signal, and the depths of water involved all mean it would need a lucky break at this stage to detect a signal. 
 
 It is still not known why the plane diverted from its planned flight path from Kuala Lumpur to Beijing four weeks ago with 239 people on board. 
 
 Race against time 
 
 Two of the ships searching an area of about 217,000 sq km (84,000 sq miles) have underwater locator capabilities. 
 
 Australian naval vessel Ocean Shield is using a "towed pinger locator" from the US Navy, while HMS Echo, which has similar capabilities, is also searching. 
 
 They are trying to detect an underwater signal emitted by the data recorders. 
 
 The battery-powered signal fades after 30 days. 
 
 The area - about 1,700km (1,000 miles) north-west of Perth - has been picked on the basis of analysis of the satellite data. 
 
 On Saturday, Malaysia announced it had set up three ministerial committees to help co-ordinate the search, and a new investigation team which would include members from Australia, China, the US, the UK and France. ||||| Media playback is unsupported on your device Media caption Air Chief Marshal Angus Houston: "Until we stop the pinger search, we will not deploy the submersible" 
 
 An Australian vessel searching for the missing Malaysia Airlines plane has detected signals consistent with those from "black box" flight recorders. 
 
 The Ocean Shield ship picked up the signal twice, once for more than two hours, said Angus Houston, a retired air chief marshal leading the search. 
 
 He called it the "most promising lead" so far. 
 
 But he said more information was needed: "We haven't found the aircraft yet and we need further confirmation." 
 
 Malaysia's acting transport minister, Hishammuddin Hussein, said he had been briefed by Air Chief Marshal Houston and was "cautiously hopeful that there will be a positive development in the next few days if not hours". 
 
 The plane, carrying 239 people, was flying from Kuala Lumpur to Beijing on 8 March when it disappeared. Malaysian officials say they believe it crashed in the southern Indian Ocean. 
 
 'Two distinct returns' 
 
 ACM Houston said the signals were detected using the towed pinger locator deployed on the Ocean Shield. 
 
 Image copyright Reuters Image caption The signals were heard by the towed pinger locator deployed by the Ocean Shield 
 
 Two separate detections occurred, he said. The first was held for two hours and 20 minutes before being lost. 
 
 Analysis "Lottery odds" is how one oceanographer described to me how incredible it would be if they had actually stumbled over distress signals from the black boxes. This listening equipment trickles along at just a few miles an hour and they were searching an area the size of Britain. Now they are racing against the clock to try to pick up the signals again so they can pinpoint a better location, and send a drone down to look for parts of the aircraft. The battery on this pinger will be starting to go flat, which cuts the range. One very interesting part of these findings is the fact that they seemed to hear two separate pings on one of their sweeps. There are two pingers on board the plane, one for each black box. Could the noise be something else? Well, the frequency of black box pings, 37.5 kHz, is designed to be unique in the water. It's an unusual frequency, so that it's easier to find. But the ocean's an incredibly noisy place and people and equipment can make mistakes. 
 
 The ship then turned around and on the return leg detected the signal again for 13 minutes. 
 
 "On this occasion two distinct pinger returns were audible. Significantly this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," ACM Houston said. 
 
 "I'm much more optimistic than I was a week ago," he said. 
 
 "We are now in a very well defined search area, which hopefully will eventually yield the information that we need to say that [Malaysia Airlines flight] MH370 might have entered the water just here." 
 
 The Ocean Shield was still in the area, about 1,040 miles (1,680 km) north-west of the Australian city of Perth, but had not been able to reacquire the signals since, he said. 
 
 The position of the signals needed to be fixed, ACM Houston said. Once that happened, the Ocean Shield could lower the Bluefin 21 underwater autonomous vehicle to try to locate wreckage on the sea floor. 
 
 The signal had been heard in sea with a depth of 4,500m, he added, which was at the limit of the capability of the Bluefin 21. 
 
 He cautioned that the next steps would take time. 
 
 "It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370," he said. "In very deep oceanic water, nothing happens fast." 
 
 The search operation is in a race against time as the flight recorders' batteries are due to run out, meaning a signal would no longer be emitted. 
 
 A Chinese search vessel, Haixun 01, also said it briefly heard signals over the weekend in a different search area. 
 
 Media playback is unsupported on your device Media caption Navy divers searched the area near the signal - courtesy Australian Defence Force 
 
 Media playback is unsupported on your device Media caption Families hold a candle-lit vigil in Kuala Lumpur, as the "black box" hunt continues 
 
 Those signals are now being investigated with the help of a British naval vessel, HMS Echo, which is equipped with sophisticated sound-locating equipment. 
 
 Reports said the crew of the Chinese ship had been using a sonar device called a hydrophone to pick up sounds. 
 
 Experts said it was technically possible but unlikely that the sounds heard with this equipment related to the missing plane. 
 
 Chris Portale, a director of the US company Dukane which makes the device that emits signals from flight recorders, said looking for the Malaysian plane's "black boxes" was like "looking for a suitcase on the side of a mountain" but under water. 
 
 But he said he thought searchers were now in the right area and had a "very good hope" of spotting debris, if the signal was from the aircraft. 
 
 "I believe they have got three to four more days of good, solid output [from the flight recorders]," he told the BBC's Today Programme. 
 
 Media playback is unsupported on your device Media caption Richard Westcott reports on the use of a pinger locator to find a black box 
 
 So far, not a single piece of wreckage has been found from the missing plane, but officials have concluded - based on satellite data - that it ended its flight in the sea to the west of Perth. 
 
 Officials do not know why it lost contact with air traffic controllers and ended up so far from its intended path. 
 
 The backgrounds of both passengers and crew have been investigated but to date officials are not thought to have discovered any concrete evidence about what might have caused the plane to disappear.
– Could it be? A Chinese ship searching for Flight 370 has picked up a ping in the southern Indian Ocean, reports CNN and the BBC. Both cite a report in China's Xinhua news agency. The pulse is 37.5 kHz, the frequency for the Malaysian plane's black-box data recorders, says the president of the beacon's manufacturer. All the reports caution that it could turn out to be yet another false hope, however. "This could be a variety of things," says one oceanographer, noting that the frequency is used by lots of instruments. For the record, the Chinese ship detected the signal at 25 degrees south latitude and 101 degrees east longitude, says the state-run Xinhua. "It is yet to be established whether it is related to the missing jet," the report says. The development comes as dozens of ships and planes intensify their sweeps in the search zone, given the finite battery life of the data recorders.