The world's largest offshore oil rig resumed sinking as rough seas impeded efforts to salvage
it four days after blasts ripped through the structure, killing 10, the Brazilian owners said on Monday.
After stabilizing the 40-story platform for a day and raising hopes it could be saved, the rig sank another 1.3 ft. (0.3 m) Sunday night and keeled over even further, Brazil's state oil giant Petrobras said.
"There is still no estimate for how long it will take to stabilize the platform," a Petrobras spokesman said.
Three explosions rocked the rig early last Thursday, killing 10 of the 175 men aboard and seriously injuring another. Petrobras, the biggest company in Brazil, was still trying to determine the cause of the explosions.
Nearly 350 engineers, divers and navy men worked around the clock, though the weather worsened as a cold front moved up the southern Atlantic seaboard to the northern coast of Rio de Janeiro state.
Meanwhile, workers unions said Monday they were stepping up protests to demand more safety. They are only going to maintain skeleton crews on the 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 a regional director for the United Oil Workers Federation.
Petrobras flew in U.S. and Dutch experts and 50 tons of European equipment to try to keep the deep-sea platform afloat and prevent an oil spill over the weekend.
They are pumping in nitrogen and compressed air and trying to pump out almost 3,000 tons of water weighing down the rig.
But rough seas with five-ft. (1.5-m) waves complicated the operation and the rig ended up sinking further beneath the surface. It has sunk almost 15 ft. (4.4 m) since the explosions and keeled over four degrees since Sunday. Petrobras is certain however that the weather is expected to improve.