Interior Minister Sandor Pinter told reporters the sludge -- which poured from the alumina factory's containment pond on Monday and rushed through villages, killing four people, injuring 120 and leaving 3 missing -- had so far been prevented from reaching the rivers.

Hungary declared a state of emergency in three counties after the sludge -- waste produced during bauxite refining which has a strong caustic effect and heavy metal content -- hit the villages of Kolontar, Devecser and others.

The cause of the spill is unknown.

"We hope we will be able to contain this," Pinter said. "At this moment we can handle the alkaline content in the river Marcal, it has not reached the river Raba."

The Marcal flows into the Raba, which flows into the Danube, a major European waterway.

Pinter said Hungary had contacted the European Union about the spill and was examining the possibility of assistance.

Reuters