The dam burst on Friday caused a sea of muddy sludge to spread across rural areas of Brumadinho city in Minas Gerais state, burying buildings and vehicles, the BBC reported.

Governor Romeu Zema said nine people were confirmed dead and there was little chance of finding people alive as rescue operations continued on Saturday.

According to reports, homes were destroyed in Brumadinho and rescue teams airlifted people covered in mud from the area due to damaged roads. It was not clear what caused the collapse of the dam, owned by Brazil's largest mining company Vale.

Many of those missing were workers who were having lunch in the dam's cafeteria that was buried by the sludge. The dam near the Feijao iron ore mine burst its barrier at around lunchtime on Friday, flooding another dam down below.

Leaked tailings from the mine spread into the nearby community of Vila Forteco, close to Brumadinho.

"Our main worry now is to quickly find out where the missing people are," Brumadinho Mayor Avimar de Melo told television channel GloboNews.

On Twitter, President Jair Bolsonaro called it a "serious tragedy" and was set to visit Minas Gerais and fly over the disaster area on Saturday, after sending three ministers there a day before.

Built in 1976, the dam was one of several in the area and it was used to hold residue from the mine. With a capacity of 12 million cubic metre the site had been lying inactive for three years, according to Vale. It was not yet known how much waste was released.

The accident came just over three years since a dam burst in another town in Minas Gerais, that killed 19 people.