|The village of Devecser in western Hungary was flooded by toxic red sludge from a local aluminium plant [AFP]
Hungary has declared a state of emergency in three counties following a toxic red mud spill that has killed four people and left another 120 injured.
A reservoir of residue from an aluminium plant broke on Monday night, releasing corrosive sludge that swamped Kolontar and Devecser, two villages in western Hungary.
"We have declared a state of emergency in Veszprem, Gyor-Moson-Sopron and Vas counties," a government spokesperson said on Tuesday.
The sludge was reported to be threatening at least another two counties.
Zoltan Illes, the environmental state secretary, said one million cubic metres of red mud had poured out of the containment pond at the Ajkai Timfoldgyar Zrt plant.
He described the incident as the worst-ever chemical accident in Hungary, saying: "It's an ecological catastrophe".
The red mud is a toxic residue left over from aluminium production and contains harmful substances such as lead, as well as highly corrosive elements.
A state of emergency was declared after a toxic mud spill killed three people and destroyed many villages
"The ceiling is three metres high, and the sludge was two metres 50 high," one local resident told state television.
"My child was at home, he managed to make a run for the roof. My father is 85, he tried to make me hold on to the window, but he had to be taken to hospital with severe leg injuries."
Rescue teams wearing protective clothing and masks worked overnight to wash the toxic substance off the streets.
Hungary's National Disaster Unit said crews were pouring plaster into a nearby river to help neutralise the spill.
"We have poured multiple tonnes of plaster into the Marcal River and hope to stem the toxic flow that way. The toxicity of the sludge moderates with every kilometre," Gyorgyi Tottos, a spokeswoman for the unit, said.
Those killed are reported to include a three-year-old child.
Many of those injured were suffering from burns and eye irritation caused by the lead and other highly corrosive elements contained in the reservoir sludge.