Casualties from a collapsed dam at a Brazilian mine have mounted after rescue teams worked through the night to find the dozens missing in mudslides that devastated a nearby village.

A spokesman for firefighters in the rescue confirmed 30 injuries and at least two deaths, but said the count was likely to rise as the search advanced slowly after mudslides knocked out roads and cellular towers.

"In reality there are a lot more, but we can't confirm any more than that. We don't even know that we'll find everybody," said firefighter Adão Severino Junior in Mariana.

He said the local hospital was "saturated" and victims arriving by helicopter were being sent to nearby Ouro Preto.

Andrew Mackenzie, Chief Executive of mine owners BHP Billiton, said a full assessment of casualties and damage was hampered by nightfall that came a few hours after the incident on Thursday.