New evacuations have been ordered at the scene of Brazil's deadly iron ore mine dam burst as the chief executives of the mining giants that own the operation made a joint visit.
The executives' visit to the Samarco mine in southeastern Brazil followed mounting pressure for answers to the November 5 disaster, which left at least six dead and 21 missing after mud mixed with mining waste poured from two tailings pond dams at the facility.
"Our priority now is to understand the extent of the consequences of the dams' rupture and what more we can do to help," said Andrew Mackenzie, chief executive of Australia-based BHP Billiton, the world's biggest mining company, and Murilo Ferreira, chief executive of Brazil's Vale, in a statement released in Portuguese.
Fears for the safety of a third dam prompted new evacuations while emergency services made repairs on Wednesday (local time). Some 631 people had already been forced from their homes in the accident.
"Families are being relocated so that they are in greater security," a spokesman for the Minas Gerais state government told AFP.
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.
Brazil's civil defence authorities called a state of emergency in the Mariana area on Wednesday, opening access to greater federal aid.
On Tuesday, authorities had ordered Samarco to step up its own measures. The joint venture is required to collect and preserve evidence related to the dam failures, making it easier for victims to be compensated.
The company will face a daily fine of about US$13,000 if it fails to comply.
Most of the village of Bento Rodrigues in the state of Minas Gerais was flattened by the wall of mud.
Fears were mounting that the sludge, which flowed into local rivers, could be toxic and contaminate the water supplies of more than half a million people in Minas Gerais and the neighbouring state of Espirito Santo.
Residents complained that the local water has a strong chemical smell, and posted photos on social media of ruined plantations and dead wildlife, including fish and turtles smothered in mud.
In Espirito Santo, a judge ordered state officials to test the Doce river water for contamination.
BHP's Mackenzie arrived in Brazil earlier this week, his presence widely seen as contrasting with the low profile kept by Ferreira. Ferreira had made an initial visit on Saturday, according to the company, although the visit was not publicised at the time.
Samarco Mineracao is a joint venture between the two mining giants.
Shares in BHP Billiton and Vale, which is the world's biggest iron ore miner, have fallen sharply since the disaster, which Deutsche Bank estimates could cost more than US$1 billion to clean up.
Minas Gerais officials ordered Samarco to halt operations. The company has put 85 percent of its employees in the two states on paid leave.