The flood of mud came without a warning.

The only hint the roughly 600 residents of Bento Rodrigues had that a sea of viscous, clay-red mud was about to flow into their village with the destructive power of lava was the deafening sound of two dams bursting Thursday afternoon at the Samarco iron ore mine in Brazil's central Minas Gerais state.

The sound sent residents running for the hills and, miraculously, most appear to have survived.

Only two people were confirmed to have been killed in the accident, which sent about 62 million cubic metres of water and iron ore tailings flooding into the village, about seven kilometres below the mine, officials said Friday. Four were injured and another 13 were missing.

However, officials warned that those numbers could rise. Only about 100 of the nearly 600 people thought to live in the area have been officially accounted for.

Cause unknown

The cause of the accident was not known, but a seismology lab at the University of Brasilia reported that several small tremors were registered in the area hours ahead of the disaster, according to O Estado de S.Paulo newspaper.

A spokesman with the U.S. Geological Survey said the agency, which monitors seismic activity worldwide, had not located any earthquakes in the region on Thursday, noting that they would generally not receive data on any event smaller than a 4.2-magnitude quake. Still, , John Bellini stressed, it would generally take a quake larger than 4.5 magnitude to damage a dam.

Whoever steps on it runs a great risk of sinking and drowning in this mud. - Fire official Vinicius Teixeira

Hundreds of survivors were taking shelter Friday in a gym in the nearby city of Mariana as donations of food, clothing and mattresses poured in. Many of the survivors had injuries to their feet, sustained after they fled their houses barefoot and trekked through the devastated terrain and then on to scorching asphalt.

Gov. Fernando Pimentel called the flood an environmental tragedy and said the accident was the "biggest natural disaster in the history of our state."

The village of Bento Rodrigues was inundated with red mud after a two dams burst last week. (Ricardo Moraes/Reuters) State prosecutor Carlos Eduardo Ferreira Pinto said he will recommend the governor suspend Samarco's environmental licence for its operations in the region.

As rescue workers evacuated the remaining survivors, the mining company's president worked to dispel fears the mud contained toxins that could contaminate the land and rivers. Ricardo Vescovi also insisted Brazilian law does not require any emergency alarm for dam failures, and that the authorities had approved the company's emergency response plan.

The public prosecutors office said it was looking into filing criminal charges against Samarco, which is jointly owned by the Brazilian mining company Vale and Australia's BHP Billiton, over the facility's lack of an emergency siren.

Sound saved lives

Resident Joaquim Teofilo Dutra confirmed that the crash of the dams giving way was the first sign of the impending disaster.

"When I went outside there were already people running uphill saying the dam burst," Dutra told The Associated Press. "All I did was close my house and run to the top."

Rescue worker Denir Ubaldo Monterio said neighbours banded together to escape the mudflow.

"As soon as the mud started to come down, the residents started helping and informing their neighbours and assisting those who had difficulties walking," he said. "When the firefighter helicopter arrived, the mud was still coming down."

The sucking mud has hampered search and rescue efforts. Still wet in patches, it acts like quicksand, O Globo newspaper quoted state fire official Vinicius Teixeira as saying.

"Whoever steps on it runs a great risk of sinking and drowning in this mud," Teixeira said, adding that it reached roof-level in some areas. "There is a risk of bodies not being found."

A representative of Mariana's mayor said Samarco officials assured them the mining company would pay for the damages, but did not provide details.