An environmental emergency has been declared in towns in two Brazilian states after a chemicals reservoir burst and contaminated two rivers.
The spillage occurred at a wood pulping factory at Cataguazes in Minas Gerais state, and much of the toxic waste is running into next-door Rio de Janeiro state.
There are warnings the environment will take years to recover
About 1.5 billion litres (396 million gallons) of caustic soda flowed into the Paraiba do Sul and Pomba rivers, according to the Rio de Janeiro state government website - although other reports have estimated the spill at 20 million litres (5.28 million gallons).
People living near the rivers have been warned not to drink or bathe in river water, amid reports that 100 animals on the river banks have already died, along with hundreds of fish.
One Brazilian newspaper warned the environment could take 10 years to recover.
The spillage occurred over the weekend and by Tuesday authorities were scrambling resources to deal with the problem.
Further spill fears
Oil workers from the federal oil company, Petrobras, were called in to help contain the spill, Ellen Alves of the Minas Gerais state environmental authority told Associated Press news agency.
She said local governments have been drilling wells and sending water trucks into the affected areas.
The spill was also affecting water supplies to the north of Rio de Janeiro state.
On Tuesday, the company responsible was fined an immediate 50 million reals ($15m) while a technical report assessing the applicable fine was prepared.
There are fears of a further spill, another Brazilian paper reported.
The Folha de Sao Paulo said the same company owned another chemicals reservoir built to the same dimensions, also containing caustic soda.
It quoted Mauro Costa, president of the state water utility company Copasa, as warning heavy rainfall could prompt another collapse.
Environment Minister Marina da Silva - herself previously an Amazon forest rubber-tapper and champion of environmental causes - warned that Brazil's new government would not tolerate lax environmental standards.
"This is a crime that can in no way go unpunished," she said.