The US coast guard has said five times as much oil as previously estimated was leaking from a well beneath the site of a drilling rig explosion in the Gulf of Mexico.
Eleven workers are missing and presumed dead after the Swiss-based Transocean Ltd's Deepwater Horizon rig sank on April 22nd, two days after it exploded and caught fire while it was finishing a well for BP about 60km southeast of the mouth of the Mississippi river.
The oil slick is threatening coastal wildlife refuges, pristine beaches and estuaries in Louisiana, Mississippi, Alabama and Florida.
The coast guard said BP - the owner of the well who is financially responsible for the cleanup - found a third leak in a well 1,500 metres under the sea off Louisiana's coast.
"BP has just briefed me of a new location of an additional breach in the riser of the deep underwater well," Coast Guard Rear Admiral Mary Landry, who is heading the federal cleanup effort, told reporters at a briefing last night.
President Barack Obama has been briefed on the situation, and "we have urged BP to leverage additional assets," including possible help from the US Defence Department, she said.
The leak is now estimated at 5,000 barrels per day - five times than previously estimated.
The leaking well has already created an oil sheen and emulsified crude slick slightly bigger than the state of West Virginia, which BP and the Coast Guard are scrambling to contain before it reaches land.
BP and the coast guard have already mounted what BP has called the largest oil spill containment operation in history, involving dozens of ships and aircraft.
After underwater robots failed to activate a cutoff valve on the ocean floor to stop the leak, BP and the coast guard yesterday set a "controlled burn" to battle a giant oil slick and prevent it from growing.
"We will not rest until we have done everything to bring this under control," said Andrew Gowers, head of group media for BP, likening the spill's consistency to "iced tea" with the thickness of a human hair.
By yesterday afternoon, the edge of the spill was 40km off the Louisiana coast, near fragile estuaries and swamps teeming with birds and other wildlife. A shift in winds could push the spill inland to the Louisiana coast by this weekend, according to forecasters at AccuWeather.
Tarballs and emulsified oil streamers could reach the Mississippi Delta region tomorrow, said Charlie Henry, an expert with the National Oceanic and Atmospheric Administration.
The spill could be devastating for fishermen and oystermen that rely on estuaries and swamps along the Mississippi River for their livelihood.
As the oil spill grows, so does the chance that it will affect efforts by the US Congress and Mr Obama to open more offshore areas to limited oil and gas drilling.
The Louisiana accident is the worst oil rig disaster since 2001, when a rig operated by Petrobras off the Brazilian coast exploded and killed 11 workers.
So far the spill is not nearly as big as the Exxon Valdez disaster, which spilled about 50 million litres of oil into the Prince William Sound in Alaska in 1989. BP's well is spewing nearly a million litres of oil a day into the ocean, the Coast Guard estimates.