State prosecutors in Brazil on Tuesday charged the ex-boss of mining giant Vale and 15 others with intentional homicide in a massive dam collapse that killed 270 people last year.

The January 25 tailings dam rupture in the mineral-rich southeastern state of Minas Gerais spewed millions of tons of mining waste over houses and farmland in the country's worst industrial accident.

Former Vale president Fabio Schvartsman is among 16 individuals charged with intentional homicide and environmental offenses, prosecutors said in a news conference.

Vale and TUV SUD, which had certified the dam's stability, have been accused of environmental crimes.

The other charged 15 people are current or former employees of the two companies.

If convicted of intentional homicide, they could face a maximum jail sentence of 30 years, prosecutors said.

The next step is for a judge to accept the charges before the prosecution can proceed.

Prosecutors accused Vale and TUV SUD of promoting "absolutely opaque risk management" between November 2017 and the day the dam collapsed.

False reports on the stability of the dam were issued and information about its "unacceptable risk" kept secret to protect Vale's reputation and market value, prosecutor William Garcia Pinto Coelho told reporters.

"The two companies imposed on society a risk that they decided society should take," Coelho said in damning remarks.

Coelho said Schvartsman, who was forced to step down soon after the tragedy, created a "false impression" of the safety of Vale's dams.

TUV SUD said in a statement earlier Tuesday it "remains deeply saddened" by the disaster.

Aerial view of Brazilian mining multinational Vale at the Corrego do Feijao mine where the collapse of a tailings dam January 25, 2019 killed 270 people
Aerial view of Brazilian mining multinational Vale at the Corrego do Feijao mine where the collapse of a tailings dam January 25, 2019 killed 270 people AFP / DOUGLAS MAGNO

It noted, however, that the "real causes" of the collapse were yet to be determined.

Vale issued a statement expressing its "perplexity" at the accusation of intent. Other agencies were still investigating and it was "premature" to make such a claim, it added.

The charges come as the town of Brumadinho, where the dam was located, prepares to mark the first anniversary of the tragedy.

So far, the official death toll is 259. Emergency workers are still searching for the bodies of 11 people listed as missing but certainly dead.

The dam breach was caused by an accumulation of water and a lack of drainage, according to a report commissioned by Vale and published last month.

Vale has been accused of failing to report defects in the structure that could have avoided the tragedy.

Brazil has since banned the construction of new upstream dams, like the one at Brumadinho, which are cheaper but less stable than other types of tailings dams. It also has ordered the decommissioning of existing ones.

Vale said it has paid nearly two billion reais (about $480 million) in compensation to relatives of the victims of the disaster.

A state court in July ordered Vale to pay for all the damage caused by the disaster, without quantifying the amount of money.

It was the second such disaster in three years involving Brazilian mining giant Vale -- one of the biggest mining companies in the world.

The failure of a tailings dam in Mariana district -- owned by a joint venture between Vale and the Anglo-Australian miner BHP -- in 2015 killed 19 people and flooded 39 towns in Brazil's worst environmental disaster