By Erica Berenstein

Venice, Louisiana - Oil from a giant Gulf of Mexico slick washed onto Louisiana shores on Saturday, threatening an environmental calamity, as two neighbouring states declared a state of emergency.

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.

US federal and state officials warned British Petroleum that its resources appeared insufficient for the task at hand as southeast winds blew the first oily strands of the slick directly onto coastal wetlands in Louisiana.

"I do have concerns that BP's resources are not adequate," said Louisiana Governor Bobby Jindal. "I urge them to seek more help from the federal government and others," he said at a press briefing.

As he issued his appeal, the neighbouring states of Alabama and Mississippi declared a state of emergency due to the imminent threat of the slick approaching their coastlines.

"With our natural resources, our businesses and our coastal communities in harm’s way, Alabama can’t afford to take anything for granted," state governor Bob Riley said in a statement.

Governor Haley Barbour of Mississippi said he had ordered the Mississippi National Guard to help local officials with the emergency response.

The oil's approach forced Louisiana to close shrimping grounds and oyster beds, as a massive effort involving state, federal and BP resources struggled to combat the slick.

Officials declined to specify the size of the spill, which measured at least 600 squares miles (1,500 square kilometres) on Wednesday when the Coast Guard said oil was leaking at a rate of 5,000 barrels a day, five times faster than previously thought.

President Barack Obama said about 1 900 federal response personnel were in the area with 300 boats and aircraft.

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

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

Salazar joined Homeland Security Secretary Janet Napolitano and Environmental Protection Agency chief Lisa Jackson in surveying the slick and containment efforts in Louisiana on Friday.

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

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

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

"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 percent of America's ecologically fragile wetlands.

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.

"It was not our accident, but it is our responsibility to clean it up," BP chief executive Tony Hayward told The Financial Times. "Where people have legitimate claims for damages, we will absolutely honour them."

At least two lawsuits have already been filed on behalf of fishermen and shrimpers, in what is expected to be a flood of litigation from the disaster.

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.

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

The Pentagon also authorised the deployment of the Louisiana National Guard, about 6 000 troops, to respond to the crisis.

Many of those dependent on the region's vital fisheries and nature reserves had already given up hope due to strong onshore squalls forecast for several days to come.

Oil was still gushing unabated from near the Deepwater Horizon platform, which sank April 22 two days after a huge explosion.

BP has been operating 10 robotic submarines in a so-far unsuccessful bid to cap the well on the seabed 1 500m below the surface.

At the Gulf well's current estimated rate of leakage, it would take 54 days for the amount of spilled toxic crude to surpass the 11 million gallons of oil that poured from the grounded Exxon Valdez tanker in Alaska in 1989. - Sapa-AFP