Workers in western Hungary raced to build an emergency dam on Sunday as cracks in a reservoir widened, threatening to unleash a second flood of toxic waste on the village of Kolontar and nearby rivers.

Officials have said it's not a matter of if but when the northern wall will collapse. Environment State Secretary Zoltan Illes said the crack, now 25 meters (82 feet) in length, had widened slightly by Sunday and that the damaged reservoir now looked to be beyond repair, according to Hungarian news agency MTI. Illes said the wall could collapse "within one day or a week."

About 1,000 people were evacuated from Kolontar on Saturday, and emergency workers are rushing to complete a new dam to protect the town and the nearby community of Devecser, home to 5,400 people.

On Monday, about one million cubic meters of toxic red sludge leaked from an alumina plant reservoir, killing seven people, injuring 123 and polluting rivers including a local branch of the Danube. The highly alkaline sludge, a byproduct of alumina production, has a caustic effect on the skin. It contains heavy metals, such as lead, and is slightly radioactive.

'Race against time'

Gyorgyi Tottos, a spokeswoman for disaster crews, said authorities hoped to complete the 600-meter dam within days. "This is a race against time as good weather is forecast for the coming few days but then the rain will come. If we can have the dam finished by the time the rain comes, then it will be all right," she said.

Monday's spill covered 1,017 hectares (2,513 acres), but Tottos said the remaining sludge was thicker and could only spread over an area of about 500 to 1,000 meters from its origin.

Prime Minister Viktor Orban has described the spill as the worst ecological catastrophe in Hungary's history. He said he will inform parliament on Monday about the findings of an investigation and promised the "toughest possible consequences" to ensure such a disaster is not repeated.

Author: Martin Kuebler (AP/Reuters)
Editor: Catherine Bolsover