New evacuations have been ordered in response to fears over the safety of a third dam at Brazil's Samarco mine, where two earlier dam breaks triggered a fatal flood of mud, officials said Wednesday.

"Families are being relocated so that they are in greater security," a spokesman for the Minas Gerais state government told AFP. Officials said emergency services were working to repair the suspect dam.

Samarco, which operates the joint iron ore venture of Australia-based BHP and Brazil's Vale, confirmed work was underway on shoring up infrastructure at the accident site.

The repairs will "bring a greater measure of stability, mitigating the effects due to the (earlier) breaking and preventing possible future problems," Samarco said in a statement.

"The authorities recommend the restricting of access to the impacted area."

The rupturing of two dams at a waste reservoir on November 5 triggered a flood that killed at least six and left 21 missing. Dozens have been driven from their homes.