Hungary declared a state of emergency on Tuesday after a toxic sludge spill swamped seven villages in what officials called the worst chemical accident in the country's history.

Up to 40 square kilometers (15.5 square miles) of land have been affected, giving rise to fears that the sludge could eventually pollute the nearby Danube River, which courses through three European capitals before flowing into the Black Sea.

"The sludge could reach the [Danube] in four or five days," said the deputy chief of the water management company for western Hungary, Sandor Toth, adding that "from the point of view of water management, it's a catastrophe."

The two-meter (6.6-foot) tide of red toxic sludge killed four people and injured 120 others on Tuesday. Eight of the injured are in serious condition and six people remain missing. Officials said on Wednesday that the death toll could rise.

The European Union would be willing to help Hungarian authorities should they need assistance in cleaning up the toxic chemical spill, EU spokesman Joe Hennon said Wednesday.

Further down the Danube in Romania, the country's Environment Ministry said it was monitoring water quality round-the-clock and stressed that the level of pollutants had not crossed the acceptable limits.

'Man-made catastrophe'

The area around Ajka, in western Hungary, was inundated with the sludge after the walls of the Ajkai Aluminia Refinery's residue reservoir, about 160 kilometers (100 miles) southwest of Budapest, broke on Monday. The plant produces alumina, which is used in the smelting of aluminum.

The red mud is a toxic residue left over from the plant's aluminum production. It is slightly radioactive, highly corrosive and contains toxic heavy metals such as lead, cadmium, arsenic and chromium. It destroyed all vegetation other than trees and seeped into hundreds of houses in seven villages, leaving residents unsure of when they would be able to return to their homes.

"This is an unprecedented incident that affects deeply the ecosystem, wetlands and surface water bodies of the region as well as pointing out the fragility of our drinking water reserves," Gabor Figeczky, the deputy country officer of the environmental group WWF Hungary, said in a statement.

Environment State Secretary Illes said there was suspicion that Hungarian Aluminum Production and Trade Company (MAL), which owns the Ajka reservoir, had stored more red sludge in the reservoir than was allowed, and that its walls had displayed stress fractures prior to the spill.

MAL chief Zoltan Bakonyi insisted, however, that the company had done nothing wrong, saying the company would suspend all production for the time being.

Prime Minister Viktor Orban, in a message to the Hungarian people on Tuesday, sent condolences to the victims' families and promised a thorough investigation to determine "who is responsible for this man-made catastrophe."

Author: Gabriel Borrud (Reuters/AFP/dpa)

Editor: Sean Sinico