Death toll sure to rise in Brazil mine disaster - mayor

So far one worker has been confirmed dead in what the governor of mineral-rich Minas Gerais described as the state's worst environmental disaster.

"The death toll will rise for sure ... The number of missing will rise because we're talking to the residents of Bento (Rodrigues) and some people still aren't accounted for," Duarte Júnior, mayor of the nearby city of Mariana, told journalists.

"What we're seeing is maybe three to six people, at the most 10 people, that are missing from Bento," he said ahead of a formal briefing scheduled on Saturday.

Walls of water filled with mining waste cascaded downhill when the dams burst on Thursday, engulfing the village of Bento Rodrigues and its 600 residents in a sea of mud while also flooding others far removed from the open-pit mine.

Towns as far as 80 kilometres (50 miles) downstream were hit by 60 million cubic meters of waste water and mudslides.

Mine operator Samarco's chief executive said a tremor in the vicinity of the mine may have caused the dams to burst, but that it was too early to establish the exact cause.

Samarco is a 50-50 venture between BHP Billiton and Brazil's Vale Samarco said it had set no date to restart the mine, which produces about 30 million tons of iron ore annually.

Output is shipped to Brazil's coast and converted into pellets for export to steel mills.

The cleanup bill and potential environmental lawsuits could be more costly than the loss of output.