A dead sea turtle is seen along the Louisiana shoreline on Saturday in Breton National Wildlife Refuge. (Eric Gay/Associated Press)

U.S. President Barack Obama called a surging oil spill, which was about 15 kilometres from the southeastern Louisiana coastline, a "massive and potentially unprecedented environmental disaster" and has promised to do whatever it takes to stop it and clean it up.

Obama made the comments Sunday in Venice, La., after seeing the growing oil slick and meeting with officials from the navy and the coast guard as well as Gov. Bobby Jindal.

"The American people are now aware, certainly, the folks down in the Gulf are aware, that we're dealing with a massive and potentially unprecedented environmental disaster," he said. "The oil that is still leaking from the well could seriously damage the economy and the environment of our Gulf states, and it could extend for a long time."

Obama also defended his administration's response to the BP oil rig explosion that's behind the 5,000 barrels of oil a day leaking into the waters, and said the three pipe leaks could take many days to stop.

While he was clear that BP PLC was responsible and that it would be paying the bill, he said the U.S. would spare no effort or resources to respond to the oil spill.

"Your government will do whatever it takes for as long as it takes to stop this crisis."

Earlier Sunday, the U.S. interior secretary spoke of a "very grave scenario" for the Gulf of Mexico coast environment as BP announced new efforts to contain its massive spill.

Ken Salazar told NBC's Meet the Press it could take three months before workers are able to stop the gush of oil from a collapsed BP-leased rig by drilling a parallel, relief well below the ocean floor.

"By the time you drill, a lot of oil could spread," he said.

"It potentially is catastrophic. I think we have to prepare for the worst," Salazar said on CNN's State of the Union.

Thousands of litres of oil have been pouring into the Gulf daily from a rupture caused when the Deepwater Horizon oil rig exploded and caught fire, 80 kilometres offshore on April 20. It sank two days later. Eleven workers are presumed to have died in the accident.

Crews operating robotic submarines have failed to shut off valves in the blowout preventer, which experts believed were badly damaged by a pressure surge that may have triggered the explosion and fire.

Skimming the oil, burning it or spiking it with chemicals to try to disperse the spill continued on the weekend with little success. Heavy waves in the open water have pushed much of the oil over containment booms.

BP chairman Lamar McKay on Sunday defended his company's safety record and said "a failed piece of equipment" was to blame for the massive spill.

'The blowout preventer was the main line of defence against this type of incident, and it failed.'—BP spokesman Steve Rinehart

"I don't think anybody foresaw the circumstance that we're faced with now," said another BP spokesman, Steve Rinehart.

"The blowout preventer was the main line of defence against this type of incident, and it failed," he said.

The 12-metre-high device typically activates after a blast or other emergency to cut off any oil that may spill.

McKay told ABC's This Week he believes a large metal and concrete box could be placed over the leak in six to eight days as a short-term measure to control the gusher.

Winds from the south have pushed the slick into Louisiana's fragile coastal wetlands.

Officials say oil could hit the shores of Alabama and Mississippi on Monday.

The National Oceanic and Atmospheric Administration has closed the waters from the Florida panhandle to the mouth of the Mississippi River to commercial and recreational fishing for the next 10 days due to the spill.