Thousands of Indonesian seaweed farmers who say Australia's worst oil spill destroyed their livelihoods are to have their class action against a Thai-owned petroleum company heard in the Federal Court.

Federal Court Justice David Yates granted the lead applicant in the class action, Indonesian seaweed farmer Daniel Sanda, an extension of time to bring the claim against PTTEP Australasia.

Daniel Sanda, an Indonesian seaweed fisherman and lead claimant in a class action over the Montara oil spill. ( Supplied: Greg Phelps )

Under Northern Territory law, class actions typically have to be lodged within three years of an incident, but Justice Yates waived that limitation.

In 2009, thousands of litres of oil spewed into the Timor Sea for 70 days straight from an uncontrolled leak at PTTEP Australasia's Montara petroleum rig.

Seaweed farmers say their harvests still have not returned to normal. ( Supplied: Greg Phelps )

The rig is in the Timor Sea, about 690 kilometres west of Darwin, and 250 kilometres southeast of Rote Island, Nusa Tenggara Timur, Indonesia - where the majority of seaweed farmers live.

The company had previously told the ABC the oil spill was contained and never reached the Indonesian coastline.

PTTEP Australasia has been contacted for a comment on the Federal Court's decision to hear the class action.

Lawyer Ben Slade, who is leading the class action on behalf of the 15,000 seaweed farmers, said their case would focus on the core issues of alleged wrongdoing and compensation.

"We are now looking forward to presenting the farmers' evidence and having it heard and determined by Justice Yates," Mr Slade said.

"This win means we can get on with the real business of securing appropriate redress for the thousands of Indonesian seaweed farmers who have had their lives severely impacted by the oil spill."