Anglo-Australian mining giant BHP can be held liable over the 2015 collapse of a dam in southeastern Brazil, London's High Court has ruled, in a lawsuit the claimants' lawyers previously valued at up to $US48.32 billion ($A74.05 billion).

Hundreds of thousands of Brazilians, dozens of local governments and around 2000 businesses sued BHP over the collapse of the Fundao dam in Mariana, southeastern Brazil, which was owned and operated by BHP and Vale's Samarco joint venture.

Brazil's worst environmental disaster unleashed a wave of toxic sludge that killed 19 people, left thousands homeless and flooded forests.

Enough mine waste to fill 13,000 Olympic-size swimming pools poured into the Doce River.

Judge Finola O'Farrell said in her ruling that continuing to raise the height of the dam

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