Eight people are dead and 150 injured after up to one million cubic metres of toxic aluminium sludge surged from an industrial plant in Ajka, western Hungary.
Some people drowned in the sludge and others suffered chemical burns.
The sludge has extinguished all life in the Marcal river and damaged nearby towns, villages and farmland.
It will have a long-term impact on health and the environment.
Police arrested Zoltan Bakonyi, chief executive of the industrial plant.
The company has been temporarily nationalised.