Firefighters have rescued 500 survivors from a torrent of mining waste that killed at least 17 people and destroyed a village after two dams burst in Brazil.
They are searching frantically for survivors after the mudslide erupted from waste reservoirs at the partly Australian-owned iron ore mine.
Officials have warned that more than 40 people could be missing.
Firefighters say they rescued 500 people who were covered in iron and mineral deposits.
BHP Billiton said it had yet to fully assess the extent of damage and casualties from the massive mudslide at Brazil's Samarco iron ore mine on Thursday night.
"Most of what happened there has been under the cloak of darkness," BHP Billiton Chief Executive Andrew Mackenzie told reporters in Melbourne. "At daybreak, clearly we will do an awful lot more and give you further updates."
The iron ore tailings dam owned 50-50 by Vale and BHP Billiton at the Germano mine near the town of Mariana in
Minas Gerais, south eastern Brazil, burst, causing the mudslide.
Civil defense authorities in Mariana said they had evacuated about 600 people to higher ground from the village of Bento Rodrigues, where television footage showed dozens of homes destroyed by the mudslide. A car rested on top of a wall where the roof of a building had been ripped off.
The mining company Samarco also said in a statement it had not yet determined why the dam burst or the extent of the disaster at its Germano mine near the town of Mariana in Minas Gerais, south eastern Brazil.
They said the flood had also reached another village further down the hill, called Paracatú de Baixo, and that inhabitants there were being evacuated.
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The dam was holding tailings, a mining waste product of metal filings, water and occasionally chemicals. It was located near the Gualaxo do Norte river, adding to fears of potential water contamination.
The G1 news service of the Globo Media group reported that between 15 and 16 people died and 45 others were missing, citing the local union.
Civil defense authorities could not confirm casualties and said numbers reported in Brazilian media were speculative. A city hall official confirmed one death and 16 injuries, adding that dozens more were missing.
Rescue crews continued to search the muddy waters after nightfall.
Brazilian army units nearby stood ready to help the search and rescue effort and the minister of national integration, Gilberto Occhi, planned to visit the state on Friday to provide assistance, according to a note from the presidency.
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Miners are struggling amid a collapse in prices of iron ore and other commodities due to concerns about demand from China, the world's top consumer of industrial raw materials.
Samarco produces about 30 million tonnes per year of iron ore, just under 10 percent of Brazil's output. Iron ore is transported down a slurry pipe from Germano to Espirito Santo, where it is turned into pellets.
BHP said it was pressing Samarco for more information and expressed concern in a statement for the safety of employees and the nearby community. Vale directed media questions to Samarco.
