A state of emergency has been declared in three western counties after the chemical waste burst from a reservoir at an alumina plant.
The spill flooded homes, roads and fields with toxic waste. Four people are known to have died, with 120 injured. Six more are missing.
At least seven villages and towns are affected including Devecser, where the torrent was 2m (6.5ft) deep.
The flood swept cars from roads and damaged bridges and houses, forcing the evacuation of hundreds of residents.
The sludge – a mixture of water and mining waste containing heavy metals – is considered hazardous, according to Hungary’s National Directorate General for Disaster Management (NDGDM).
Some 600,000-700,000 cubic metres (21m-24m cubic feet) of sludge escaped from the plant, 160km (100 miles) from the capital, Budapest.
Full story: BBC News – Hungary battles to stem torrent of toxic sludge