Authorities have ordered thousands to evacuate from a dam at risk of giving way in south-eastern Brazil, just days after a nearby dam collapsed.
At least 37 have been killed and more than 250 others are feared dead in Friday’s disaster at an iron ore mine near the town of Brumadinho.
Rescue operations have been suspended after officials warned of dangerously high water levels at the second dam.
Both dams at the mining complex belong to Vale, Brazil’s largest mining firm.
Warning sirens rang out at 5:30 local time (7:30 GMT) over Brumadinho, which is home to some 39,000 people.
All the town’s bridges have been ordered to close, while residents rush to higher ground.
“With bags on their backs, everything they could grab, children, old people climbing up, it was total despair,” one man told the BBC.
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The rupture of the dam on Friday caused a sea of muddy sludge to bury the site’s cafeteria, where workers were eating lunch, and at least one bus that carried employees, before engulfing buildings, vehicles and roads.
On Saturday, emergency services used helicopters and earth-moving machinery in the search for survivors.
Rescue efforts were suspended on Sunday over fears of the second dam bursting, according to reports.
Some 366 people have been rescued, Minas Gerais state fire department says. Of those, 23 have been taken to hospital.
Vale said it could not reach 252 of its employees and contractors. Residents and guests at an inn were also reported missing.
Eight of the victims have been identified.
