Indonesian seaweed farmers launched a Aus$200 million class action Wednesday over a major oil spill in Australia, claiming the blow-out devastated their livelihoods.

The spill in the Montara field in the Timor Sea, north of Australia, leaked thousands of barrels of oil for close to 10 weeks before it was capped.

The case filed in Sydney's Federal Court on behalf of up to 13,000 Indonesian farmers is against the firm which operated the well-head platform, PTTEP Australasia.

Ben Slade, class actions principal at law firm Maurice Blackburn in Sydney, said the huge spill was still impacting farmers in the eastern Indonesian province of Nusa Tenggara Timur.

"If the company thought that this issue would go away because the farmers are Indonesians, or because they didn't understand their legal rights, they were sorely mistaken," he said in a statement.

"This case is a perfect example of how the Australian class action regime provides access to justice for people who would otherwise have no voice and no recourse against their corporate wrongdoer."

An Australian government report found the spill was caused by shortcomings at PTTEP Australasia, a unit of Thailand's PTT Exploration and Production PCL.

PTTEP said it will defend the action, worth the equivalent of US$152 million, which it believes is misguided.

"The company has always accepted responsibility for the 2009 Montara incident," it said in a statement, adding that modelling had concluded 98 percent of the oil had stayed in Australian waters.

PTTEP said comprehensive studies clearly showed "no lasting impact on the highly sensitive and biodiverse ecosystems in the areas closest to Indonesian waters".

The leak, more than 200 kilometres (124 miles) off Australia's northwest coast, was the worst the country has seen from an offshore oil platform.

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PTT EXPLORATION & PRODUCTION