Oil from a giant Gulf of Mexico slick began washing onto Louisiana shores yesterday, threatening an environmental calamity as President Barack Obama called for a "thorough review" of the disaster.

With up to 200,000 gallons of oil a day spewing into the Gulf of Mexico from a ruptured well, the accident stemming from a sunken offshore rig may soon rival the Exxon Valdez disaster as the worst oil spill in US history.

Strong southeast winds blew the first oily strands of the slick directly onto the coastal wetlands of South Pass near the mouth of the Mississippi river late Thursday, Billy Nungesser, president of Plaquemines Parish, where oil washed ashore, said.

Fresh water from the Mississippi River was being diverted into wetlands in an attempt to push back some of the oil, Wilma Subra of the Louisiana Environmental Action Network said.

"This is a very, very good measure," she said, as hundreds of miles of coastline came under threat in Louisiana, Mississippi, Alabama and Florida, a region that amounts to more than 40 per cent of America's ecologically fragile wetlands.

Louisiana shrimping grounds and oyster beds were being closed, the state's Governor Bobby Jindal said at a press briefing yesterday, adding that he was concerned clean up resources provided by British Petroleum were inadequate.

Mr Obama said some 1,900 federal response personnel are in the area with 300 boats and aircraft to combat a slick measuring at least 1,500 square kilometres.

"We've laid 217,000 feet of protected boom and there are more on the way," Mr Obama said in Washington.

The President said he asked Interior Secretary Ken Salazar "to conduct a thorough review of this incident and report back to me on 30 days" on precautions required to prevent a recurrence of such a disaster.

The White House said new domestic offshore oil drilling was on hold until the disaster had been fully investigated and dispatched teams to the Gulf Coast "to inspect all deep water rigs and platforms to address safety concerns."

British energy giant BP said meanwhile it is "taking full responsibility" for the Gulf of Mexico oil spill and will pay for "legitimate claims" stemming from the disaster.

Company spokeswoman Sheila William said the energy firm was ready to assume costs related to the cleanup and to reimburse damages suffered from what could become one of the worst oil spills in history.

However Homeland Security Secretary Janet Napolitano yesterday pressed BP to do more to stop the slick.

"We continue it urge BP to leverage additional assets to help lead the response in this effort," she said.

The region is a prime spawning ground for fish, shrimp and crabs, home to oyster beds and a major stop for migratory birds.

"For birds, the timing could not be worse; they are breeding, nesting and especially vulnerable in many of the places where the oil could come ashore," said Melanie Driscoll of the Audubon Society, a nature conservancy group.

The Coast Guard was coordinating vessels including skimmers, tug boats and robotic submarines, which are investigating the underwater damage.

With the ruptured well no closer to being capped, the White House went into emergency response mode to try and avoid the kind of disaster that Hurricane Katrina brought to the region in 2005.

US officials called the event a disaster of "national significance" to better coordinate resources, as the governors of Louisiana and Florida declared states of emergency. Mr Jindal also sought the mobilisation of 6,000 National Guard troops to respond to the crisis.

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