A state of emergency has been declared in western Hungary following the escape of large amounts of toxic sludge from an alumina plant.
Emergency services are trying to prevent the sea of red mud getting into nearby waterways, including the Danube.
At least four people have died and 120 are injured, while six more are missing.
At least seven villages and towns are affected including Devecser, where the torrent stood two metres deep.
The flood swept cars from roads and damaged bridges and houses, forcing the evacuation of hundreds of residents.
One witness said his uncle was taken to hospital by helicopter after the sludge burnt him to the bone, the BBC reported.
The sludge is a mixture of water and mining waste containing heavy metals.
Others suffered burns and eye irritations caused by lead and other corrosive elements in the mud.
Some 600,000-700,000 cubic metres of the sludge escaped from the plant, 160km from the capital, Budapest.
With 7,000 people affected directly by the disaster, a state of emergency was declared in the county of Veszprem where the spill occurred, and Gyor-Moson-Sopron and Vas, where the sludge appeared to be heading.
At least 390 residents have been relocated and 110 rescued from flooded areas, the Natural Disaster Unit (NDU) said.
The waste burst out of a containment reservoir at the plant, owned by MAL Zrt.
Prime Minister Viktor Orban said the spill may have been caused by human error. He said tests had shown there was no threat of radiation.
People in Kolontar, which lies closest to the burst reservoir, were trying to recover their belongings but police were not yet letting them back into their flooded homes.
"My bathtub is full of this sludge ... when the dam burst, it made a terrible noise. I was in my yard, and I had to run up the steps to the porch but the water was rising faster than I could run," Ferenc Steszli, 60, told Reuters. He said he escaped by standing on a table.
Farmland around the village was covered in the sludge and many livestock were killed.
The disaster unit said clean-up crews were pouring plaster into a nearby river to help neutralise the spill and attempts were being made to prevent the sludge getting into the Danube, a major European waterway.
MAL Zrt said in a statement there had been no sign of the impending disaster and that the red sludge did not qualify as hazardous waste according to European Union standards.
The NDU defined the red mud on its website as: "A by-product of alumina production. The thick, highly alkaline substance has a caustic effect on the skin. The sludge contains heavy metals, such as lead, and is slightly radioactive. Inhaling its dust can cause lung cancer."
It recommended people clean off the sludge with water to neutralise the substance.