At least one dead and dozens missing after dam holding back waste water from an iron ore mine burst in Mariana city.

A dam holding back waste water from an iron ore mine in the southeastern Minas Gerais state has burst, devastating a nearby town with mudslides and leaving officials in the remote region scrambling to assess casualties.

“The number of missing is going to surpass 40 but that is not official,” Adao Severino Junior, fire chief in the city of Mariana, told AFP news agency on Thursday.

Civil defence authorities told Reuters that casualties were still not confirmed and that numbers reported in Brazilian media were speculative. A city hall official confirmed one death and 16 injuries, adding that dozens more were missing.

Rescue crews continued to search the muddy waters after nightfall.

Brazilian army units nearby stood ready to help the search and rescue effort and the minister of national integration, Gilberto Occhi, planned to visit the state on Friday to provide assistance, according to a note from the presidency.

The mining company Samarco, a joint venture between top iron ore miners Brazil’s Vale and Australia’s BHP, said in a statement it had not yet determined why the dam burst or the extent of the disaster at its Germano mine near the town of Mariana in Minas Gerais, southeastern Brazil.

Civil defence authorities in Mariana said it was evacuating about 600 people to higher ground from the village of Bento Rodrigues, where television footage showed dozens of homes destroyed by the mudslide. A car rested on top of a wall where the roof of a building had been ripped off.

They said the flood had also reached another village further down the hill, called Paracatú de Baixo, and that inhabitants there were being evacuated.

The dam was holding tailings, a mining waste product of metal filings, water and occasionally chemicals. It was located near the Gualaxo do Norte river, adding to fears of potential water contamination.