Cleanup is underway after an aluminium plant's reservoir collapsed.
An aluminum plant's industrial waste has spilled through seven villages.
The mud is slightly radioactive and highly corrosive. It also contains toxic heavy metals.
Two adults and two children were killed.
Locals in Devecser, Hungary, are salvaging what they can after an aluminium plant's toxic waste reservoir collapsed, killing four people and flooding seven nearby towns.
AP Photo/Bela Szandelszky
Hungary scrambled Wednesday to contain a toxic mud spill that left four people dead and more than 100 injured in what is being described as an ecological catastrophe.
The accident occurred Monday when the retaining walls of a reservoir at an aluminum plant in Ajka in western Hungary collapsed, unleashing a toxic soup of industrial waste through seven villages.
The devastation spread across an area of 40 square kilometers (15.4 square miles) in what officials say is Hungary's worst-ever chemical accident that has so far killed two adults and two children.
The wave overturned cars, swept away possessions and raised fears that pollution leeching from it could reach the Danube River, which courses through Croatia, Serbia, Bulgaria, Romania and Ukraine before flowing into the Black Sea.
The mud -- a residue from aluminum production which is slightly radioactive, highly corrosive and contains toxic heavy metals such as lead, cadmium, arsenic and chromium -- destroyed all vegetation other than trees and seeped into hundreds of houses in the villages and contaminated waterways.
A spokeswoman for the disaster relief services, Timea Petroczi, said Wednesday efforts to neutralize the pollution in rivers was "already getting good results showing that alkaline levels in the water are falling."
"We've got 500 people involved in the clean-up today. We're using high-pressure water jets to clean roads and houses."
While the death toll has not risen so far, out of 123 injured, eight people are in serious condition in hospital suffering from burns and another 53 also remain hospitalized.
Originally, six people had been feared missing, but that number has been revised downwards to three, Petroczi said.
Eyewitnesses say the force of the wave was so strong that cars were sucked out from their garages and it tore down doors and windows, covering everything.
"I've lost everything. We've lost everything," said one man standing in front of the remains of his house, which he had just spent 5,000 euros ($6,900 dollars) in renovating.
"Last week was the first time we slept in our new bed with my eight-month pregnant wife who was taken to hospital with burns from the sludge," he said.
Environment state secretary Zoltan Illes, who visited the area on Tuesday, described the accident as "an ecological catastrophe" and the worst chemical accident in the country's history.
Interior Minister Sandor Pinter warned the sludge "can cause burns to the skin and blindness if it gets into your eyes."
According to an expert quoted by the Hungarian news agency MTI, the pollution had been due to reach the county of Gyor-Moson-Sopron by midday Wednesday, bringing it closer to the Danube.
Nevertheless, thanks to rain and the neutralizing agents used so far "alkaline levels in the Marcal River are already falling and the connecting Raba will suffer much less damage" than feared, he said.
Environmental group Greenpeace said it had taken samples which showed the presence of lead, chrome and arsenic in water in the area.
But it would await further samples in the afternoon before deciding on a plan of action, said spokesman Marton Vay.
Petroczi confirmed the drinking water system had not been affected, but "as a precautionary measure, people are not allowed to use the water wells."
Residents were also banned from eating any home-grown produce or from hunting or fishing in the region, she said.
Two days after the disaster, cars, debris, dead animals still litter the streets and fields.
"It is still chaos here, nobody knows what to do or where to start," said one volunteer worker, who preferred to not to give his name.
"I think it's a disgrace. Things are going so slowly. The flood was on Monday and now on Wednesday we're still waiting for orders."