The Hungarian government declared a state of emergency in several towns Tuesday, a day after a reservoir at an alumina refining plant in Ajka burst its banks, unleashing a flood of caustic red sludge that killed at least four people and injured more than 120, government officials said. The flood, estimated at 700,000 cubic meters, or 185 million gallons, swept cars off roads, damaged bridges and houses and forced the evacuation of hundreds of residents. People who came in contact with the substance were burned through their clothes. 'People here speak of a mini-tsunami,' said Gyorgy Bakos, spokesman for the National Directorate General for Disaster Management, who was close to the scene of the accident. Hungarian environmental experts said that the spill could have devastating environmental consequences and that it threatened to pollute the Danube River, causing long-term damage to ecosystems and killing fish and vegetation. The agricultural soil that is now under the sludge will have to be replaced at a potentially high cost, the experts said. The authorities and emergency services evacuated residents from Kolontar, Devecser and Somlovasarhely, in southwestern Hungary, and set up makeshift camps in schools and local community centers. In addition to the dead, who appeared to have drowned, five people were missing, and a total of 7,000 residents were affected by the spill. About 60 people were hospitalized, according to the National Directorate General for Disaster Management. Zoltan Illes, state secretary at the Environment Ministry, who was also in Devecser, called the spill an 'environmental disaster.' The sludge leaked and flooded the towns through the Torna River. Some 270 homes were quickly engulfed. The sludge spread over 16 square miles, according to the Environment Ministry. Gabor Figeczky, deputy country officer of WWF-Hungary, an environmental group, said that the main threat from sludge was that it is very alkaline, with a pH as high as 13, making it a caustic detergent that could burn, which had led to the injuries. Figeczky said the environmental risk was created by the highly alkaline substance flowing into rivers and killing all life there. He said it was the first large spill of such sludge, and it remained unclear whether rainfall and upstream water could help dilute the caustic mud in the river and avert more damage in the larger rivers downstream. 'There hasn't been such a spill of this red sludge before anywhere,' he said. The Hungarian Environment Ministry immediately ordered the owner of the Ajka alumina plant, MAL Zrt, the Hungarian Aluminum Production and Trade Company, to suspend all operations. Viktor Orban, the prime minister, appealed for calm. 'There are grounds for panic, and this is understandable,' he told reporters. He said the government had set up a special team of experts to analyze the accident, which he said might have been caused by human error and showed no signs of having been the result of natural causes. He stressed that there was no threat of radiation in the area affected by sludge. Red sludge, also known as red mud, is a byproduct of the refining of bauxite into alumina, the basic material for manufacturing aluminum, according to the Aluminum Association, an industry trade group based in Arlington, Va. The sludge, a waste product, contains heavy metals and is toxic if ingested, scientists say. The plant's owner issued a statement Tuesday afternoon saying that 'the red sludge waste is not considered hazardous waste' according to European Union standards. The company added that it had conformed to all safety standards. Joseph Hennon, European Commission spokesman for the environment, said the sludge was regulated under commission law but was not necessarily considered a hazardous waste; that depends on what exactly it contains. He said the commission was waiting for the Hungarian government to provide an analysis of the sludge. The factory received a permit for handling the sludge from the Hungarian government in 2006. 'It presumably had procedures for handling and safety,' he said. According to the Aluminum Association, the alumina refining process removes impurities from the bauxite-containing soil, leaving a residue that is highly alkaline and caustic. Generally, the residue is washed several times to reduce the alkalinity and remove potentially hazardous materials, and then dried, according to the association. The final material contains trace amounts of nearly every element found in the Earth's crust, but the U.S. Environmental Protection Agency does not consider red mud a toxic or carcinogenic substance, an association official said. Residents in Kolontar, not far from where the accident occurred, tried to rush from their homes as a wave of sludge 6 feet high pushed its way through narrow streets and homes. 'My dad, who is 82 years old, managed to lift up my mother to the level of the window, holding her tight,' Robert Lemann, a local resident, told Hungarian public television. 'Then we rushed my father to the hospital because the alkaline burned the skin on his legs.' Others complained that they had lost their livelihoods as farms, family corner shops and local businesses were overcome by the onslaught of the red sludge. Bakos said any residents who came in contact with the sludge experienced unpleasant sensations to the legs, arms or ears. Officials said it was hard to confirm the numbers, but 80 to 120 people were taken to the hospital for treatment. 'It is chaotic here in the sense that people do not know how to react,' he added. But some people, fearing for their property and possessions, were eager to return. 'They are concerned about their valuables, their assets,' he said. 