The wall of the reservoir could collapse within a day or a week, Environment State Secretary Zoltan Illes said.

BBC: Hungary builds wall to slow possible new sludge wave

"We've got the World Cup in 2014 and then the Olympics, " says Paulo Illes, a coordinator at the center.

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Mr Illes said a layer of soil 2cm deep (0.8 inches) would need to be removed from the whole of the contaminated region.

BBC: 'One year' to clean toxic spill in Hungary

"Once the rain is here, the remaining sludge will be washed out and the the dam's northern sections is going to break away, " Mr Illes said.

BBC: Hungary builds wall to slow possible new sludge wave

Environment Minister Zoltan Illes told the BBC the clean-up would take at least one year and probably require technical and financial assistance from the European Union.

BBC: 'One year' to clean toxic spill in Hungary

An alert has been declared for the Marcal and Torna rivers, and Mr Illes said workers were "desperately" trying to stop contamination of the Raba and Danube rivers.

BBC: 'One year' to clean toxic spill in Hungary

Hungarian media quoted Mr Illes as saying that a 25-metre-long crack in the weakened wall of the reservoir near Ajka had widened slightly by Sunday morning and that the wall of the damaged reservoir now looked beyond repair.

BBC: Hungary builds wall to slow possible new sludge wave