Oil from a leaking well in the Gulf of Mexico began washing ashore in the southern US state of Louisiana, threatening an ecological disaster.
Blown by strong southeast winds, a sheen of oil reached the fragile coastal wetlands of South Pass near the mouth of the Mississippi river, said Billy Nungesser, president of Plaquemines Parish, where the oil first hit the shoreline.
It marks the beginning of what environmentalists fear could be one of the worst US ecological disasters in years, with experts still unable to cap the ruptured underwater well which federal officials estimate is spewing about 200,000 gallons of oil per day into the Gulf.
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An officer with the US Coast Guard, which is helping coordinate the response to the widening disaster, late Thursday would not confirm that the oil had reached the Louisiana coastline.
"We have BP teams out in the field trying to confirm those reports." Coast Guard Petty Officer Erik Swanson said.
Government declared national disaster
The US government declared a national disaster Thursday as the giant oil slick threatened to wreak economic and environmental havoc along hundreds of miles of the US Gulf Coast, following a deadly explosion April 20 on an oil rig leased by British Petroleum (BP).
The rig collapsed two days later, and three leaks were discovered in the well head and the riser pipe that had connected the rig to the well more than 5,000 feet (1,500 meters) below the surface.
The Gulf Coast region is teeming with hundreds of species of wildlife, and is also home to a massive fishing and seafood industry which experts warn could be ruined should authorities fail to prevent the spill from spreading.
Obama weighs in
Earlier US President Barack Obama sent senior members of his cabinet and interior chiefs to survey the damage.
"Homeland Security Secretary Janet Napolitano, Department of the Interior Secretary Ken Salazar and Environmental Protection Agency Administrator Lisa Jackson will... inspect ongoing operations dedicated to minimising environmental risks in the areas affected by leaking oil," a statement said on Thursday.
British Petroleum, which leased the rig, has led a multi-pronged effort to contain and collect the spilt oil, but efforts to corral it and burn it off failed amid worsening weather.
Strengthening winds are now blowing 1550-square-kilometre slick directly onto the Louisiana coast, where a rich variety of wildlife is at risk in the maze of marshes that account for 40 per cent of all US wetlands.
Napolitano, Salazar and Jackson "will conduct an aerial tour of the affected area in the Gulf of Mexico to view BP's cleanup and containment efforts firsthand," said the statement issued by the joint command centre overseeing the containment effort.
