More than 7000 people from the Papua New Guinea province of Madang are suing a mining company for damages worth US$5.3 billion.
Last year, 200,000 litres of toxic slurry spilled into the ocean from the Basamuk nickel refinery, turning the sea red and killing marine life.
But the plaintiffs - who include villagers, scientists, chiefs and the provincial government - claim the company, Ramu Nico, had been causing environmental damage for years.
The lawyer leading the suit, Ben Lomai, said the plaintiffs wanted the court to declare Ramu Nico a public nuisance, and that it acted negligently.
He said the spill injured peoples' enjoyment of their customary land and water rights.
"We are basically alleging that the tort of nuisance, public nuisance and private nuisance; we're also alleging the tort of strict liability and at the same time we're also alleging the tort of negligence. We're saying for their land and water to be contaminated, that is in breach of the plaintiffs' rights."