Emergency workers and construction crews in Hungary are struggling to clear roads and homes hit by a spill of toxic red sludge.
Hundreds of people were evacuated after the disaster, when a gigantic sludge reservoir burst its banks at a metals plant in Ajka, a town 100 miles south-west of Budapest.
The torrent inundated homes, swept cars off roads and damaged bridges, disgorging an estimated one million cubic metres of toxic waste onto several nearby towns.
Hungarian officials have declared a state of emergency, calling the spill "an ecological disaster" that could threaten the Danube River, one of Europe's great waterways.
At least four people have been killed by the sludge, three were still missing and 120 injured, many with burns.
Meanwhile, the European Union warned the spill could also turn into an ecological disaster in other nations.
EU spokesman Joe Hennon said the EU stood ready to help if the disaster took on bigger proportions. "We are concerned, not just for the environment in Hungary, but this could potentially cross borders," He said.
With the Danube flowing through Croatia, Serbia, Romania, Bulgaria, Ukraine and Moldova before spilling into the Black Sea, there is the potential for widespread serious environmental damage.
Emergency workers wearing masks and chemical protection gear also rushed to pour 1,000 tons of plaster into the Marcal River in an attempt to bind the sludge and keep it from flowing on to the Danube, 45 miles away.
Named for its bright red colour, the material is a waste product in aluminium production that contains heavy metals and is toxic if ingested.