DEVECSER, Hungary — Hungary declared a state of emergency in three counties Tuesday after a flood of toxic red sludge from an alumina plant engulfed several towns and burned people through their clothes. One official called it “an ecological disaster” that may threaten the Danube and other key rivers.

The toll rose to four dead, six missing and at least 120 people injured after a reservoir failed Monday at the Ajkai Timfoldgyar plant in Ajka, a town 100 miles southwest of Budapest.

Several hundred tons of plaster were being poured into the Marcal River to bind the toxic sludge and prevent it from flowing on, the National Disaster Management Directorate said.

So far, about 35 million cubic feet of sludge has leaked from the reservoir, affecting an estimated 15 square miles, Environmental Affairs State Secretary Zoltan Illes told the state news wire MTI.

Illes called the flood an “ecological catastrophe” and said the sludge could reach the Raba and Danube rivers. He suspended activity at the plant and ordered the company to repair the damaged reservoir.

The disaster agency said 390 residents had to be temporarily relocated and 110 were rescued from the flooded towns, including Kolontal, Devecser and Somlovasarhely.

Firefighters and soldiers swept through the region Tuesday carrying out cleanup tasks with bulldozers.

The sludge, a waste product in aluminum production, contains heavy metals and is toxic if ingested.

Many of the injured sustained burns as the sludge seeped through their clothes, and two faced life-threatening conditions.

Two women, a young man and a 3-year-old child were killed in the flooding.

In Devecser, the sludge in Tunde Erdelyi’s house was still five feet high Tuesday and rescue workers had to use an ax to cut through her living room door to let the red liquid flow out.