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 thick 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 intends to 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 the UK legal action in 2018 to demand compensation from BHP. At the time of the disaster, one of its global headquarters was in Britain.

The eventual trial at the High Court in London 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 ruled on Friday that "BHP were negligent, imprudent and/or lacking in skill," in monitoring the dam's condition, despite studies and recommendations for remediation.

"The risk of collapse of the dam was foreseeable," she noted in the judgment.

- 'Long-overdue justice' -

BHP maintained on Friday 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 to be awarded to claimants will be decided at a later trial, scheduled for October 2026.

The city of Mariana, one of the areas hardest hit by the disaster, is seeking tens of billions of Brazilian reais in damages.

"Today's ruling delivers long-overdue justice to the thousands whose lives were torn apart," said Pogust Goodhead chief executive Alicia Alinia.

She added that the judgment "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.

"Finally, justice has begun to be served, and those responsible have been held accountable for destroying our lives," Gelvana Rodrigues, who lost her 7-year-old son in the tragedy, said in a statement shared by Pogust Goodhead.

"I promised myself that I would not rest until those responsible were punished for the death of my son Thiago," she said.

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