DEVECSER, Hungary – The cracking wall of an industrial plant reservoir appeared on the verge of collapse late Saturday, and engineers were working to blunt a possible second wave of the caustic red sludge that has already deluged several towns in western Hungary.

Residents of one nearby town were evacuated, others were ordered to be ready to evacuate and everyone was bracing for a new onslaught of toxic material.

“If another wave comes, I was thinking of standing on top of the kitchen table,” said Maria Gyori, 79, a homemaker in the town of Devecser. “Maybe the sludge won’t go that high.”

Prime Minister Viktor Orban said the northern wall of MAL Rt.’s storage pool, which released at least 184 million gallons of caustic red sludge and water five days ago after one of its corners ruptured, was showing numerous cracks and seemed ready to fail completely.

“Because it may happen at any moment, but it’s also possible that it won’t happen there’s only one thing we can do — we have to behave as if this could happen any minute,” Orban told reporters in Budapest. “There’s no technical equipment that could really stop this process, and the only thing we can do is prepare ourselves to stop the damage it would cause.”

Engineers were building retaining walls around the previous breach and the weakened wall of the reservoir just outside Kolontar, the town hardest hit by the sludge flood. Kolontar’s nearly 800 residents were evacuated early Saturday as a preventive measure.

On Monday, the highly polluted water and mud flooded three villages in less than an hour, burning people and animals. At least seven people were killed and at least 120 were injured. Several of those who were hospitalized were in serious condition.

Orban said the latest dams, in the direction of lower-lying populated areas, were meant to slow the mud in case of a second rupture and give officials time to warn the population.

The roughly 6,000 residents of Devecser, 2.5 miles north of Kolontar — and that much farther away from the reservoir — were told by police to pack a single bag and get ready to leave at a moment’s notice.

The premier said experts had estimated that 132 million gallons of red sludge could escape from the reservoir if the wall collapsed, but said exact figures were hard to calculate.

“We have no exact information about the nature of the material because a catastrophe like this has never happened before anywhere in the world,” Orban said Saturday in Ajka, a city to which many Kolontar residents were taken.

Red sludge is a byproduct of the refining of bauxite into alumina, the basic material for manufacturing aluminum. Treated sludge is often stored in ponds where the water eventually evaporates, leaving behind a largely safe red clay. Industry experts say the sludge in Hungary appears to have been insufficiently treated, if at all, meaning it remained highly caustic.