New fears of Brazil oil spill

Three blasts rocked the rig killing 10 workers aboard

The world's largest oil rig has started sinking again as rough seas hampered efforts to save the platform.

There is still no estimate for how long it will take to stabilise the platform

Petrobras spokesman

The 40-storey structure has sunk more than 4.5 metres (15 feet) since a series of explosions damaged one of the support columns on Thursday, killing at least 10 workers.

Salvage teams trying to pump out water by forcing compressed air and nitrogen into the column are having difficulty reaching the most important compartments some 50 metres below the surface.

The platform has up to 9,500 barrels (1.5 million litres) of oil on board which could leak out if the platform sinks entirely.

The rig had stabilised for one day, raising hopes that it could be saved, but on Sunday night it keeled over even further.

However, a spokesman for the state oil giant Petrobras said it was still possible for the P-36 rig to be salvaged, if the bad weather passes quickly as expected.

But he said: "There is still no estimate for how long it will take to stabilise the platform."

Petrobras has flown in US and Dutch experts as well as special equipment from Europe to try to save the $350m rig.

Petrobras said it was still trying to determine the cause of the explosions, which local media reports say were caused by a gas leak.

'No leaks'

Only one body has been recovered from the rig so far.

P-36 rig: "A model of Petrobras' deepwater production expertise"

The salvage teams have still not been able to gain access to the submerged pillar where the bodies of eight fire-fighters - missing since last week's explosion - are believed to be trapped.

Petrobras said that so far no oil has leaked from the damaged structure, which is 120km (75 miles) off the Brazilian coast.

The oil company has been struggling to rebuild its reputation after two major oil spills and accidents which killed 81 workers.

Petrobras hall of shame

1984: 34 people killed in oil platform explosion and fire

35 oil workers killed since 1998 at Petrobras facilities, say unions

Jan 2000: One million litres of oil from tanker polluted Rio de Janeiro's picture-postcard Guanabara Bay. Fined $28m

July 2000: 4 million litres of crude oil spilled from a broken pipeline into the Iguacu river in southern Brazil. Fined $110m

Workers' unions say they are stepping up protests to demand better safety procedures.

Skeleton crews are operating on 50 platforms in the Campos Basin off the Rio coast, which supplies around 80% percent of Brazil's oil.

"The protest is for life, for health, safety and in the memory of our lost colleagues," said Fernando de Carvalho, a regional director for the United Oil Workers Federation.

Petrobras had hoped the P-36 rig would be a demonstration of its deepwater production expertise.

It began operations last year and was pumping 80,000 barrels of oil per day, less than half its projected capacity and about 5% of Brazil's total output.

Petrobras said the shortfall in oil output that is now expected will cost Brazil some $50m a month in oil imports.