A dam collapse in 2015 at an iron-ore mine run by a firm co-owned by BHP killed 19 people and unleashed a deluge of toxic mud into villages, fields, rainforest, rivers and the ocean.

"BHP are strictly liable as 'polluters' in respect of damage caused by the collapse," the High Court in London said in its ruling following a mammoth trial.

BHP on Friday said it would appeal the ruling.

"BHP has supported extensive remediation and compensation efforts in Brazil since 2015," the company said in a statement.

The victims first filed a UK legal action in 2018 demanding compensation from BHP. At the time of the disaster, one of its global headquarters was in Britain.

The eventual trial at the High Court ran from October 2024 to March this year, and the court has already begun preparing the second phase of the case to determine potential damages and compensation.

During the trial, the claimants' lawyers argued that BHP was aware that toxic sludge was accumulating at the facility in Minas Gerais state, north of Rio de Janeiro, at rates that far exceeded the annual limit.

The lawyers said the build-up contributed to the disaster at the mine, which was managed by Samarco, co-owned by BHP and Brazilian miner Vale.

Judge Finola O'Farrell said BHP had been negligent in monitoring the dam's condition, despite studies and warnings recommending remediation.

"The risk of collapse of the dam was foreseeable," she said.

- 'Now I can be okay' -

Pamela Sena, 31, a housewife and manicurist in Bento Rodrigues -- one of the hardest-hit villages -- said she "started crying with happiness" when she learned of the ruling.

She told AFP of her last morning spent with her family before the torrent of toxic mud killed her five-year-old daughter Manuela in the village of Bento Rodrigues.

The daughter was at school that day when Sena got a warning to flee to higher ground as the mud approached. She was told her family was already safely at the highest point of the village.

"But when I got there, they weren't there. And when I looked down, everything was already destroyed," she told AFP. Her husband and son were later found alive.

"Besides losing Manu, our memories, her story, her photos, everything we had went away with the mud. There's nothing left."

She said while no money could bring her daughter back, she was delighted to see justice done after "10 years of struggle, of humiliation after humiliation."

"I needed to hear that justice would be done so I could be okay, and now I can be okay."

- Companies cannot just 'walk away' -

BHP maintained that a compensation agreement it reached last year in Brazil -- worth around $31 billion -- provided a resolution.

However, a majority of the 620,000 claimants, including 31 municipalities, argue that they are not sufficiently covered by the deal.

Instead, claimants are seeking around pound36 billion ($47 billion) in compensation, according to a previous estimate from law firm Pogust Goodhead.

The amount of compensation will be decided at a trial scheduled for October 2026.

Pogust Goodhead chief executive Alicia Alinia said the judgement "sends an unmistakable message to multinational companies around the world: You cannot disregard your duty of care and walk away from the devastation you caused."

Vale and BHP were acquitted in November 2024 of criminal charges by a Brazilian court, which ruled there was insufficient evidence linking them to the dam's failure.

Another similar civil lawsuit has been ongoing since 2024 in the Netherlands.