The US Coast Guard says five times as much oil as previously thought could be leaking from a well beneath where a rig sank in the Gulf of Mexico last week, BBC reported.
Rear Admiral Mary Landry said 5,000 barrels (210,000 gallons) a day were now thought to be gushing into the sea 50 miles (80km) off Louisiana's coast. A third leak had also been discovered at the site, Adm Landry said.
Earlier, a Coast Guard crew set fire to part of the oil slick, in an attempt to save environmentally fragile wetlands. The "controlled burn" of surface oil took place in an area about 30 miles (50km) east of the Mississippi river delta, officials said. Weather forecasters have meanwhile warned that changing winds could drive the oil slick ashore by Friday night.
The leak now appears so great that it's calculated that in less than two months it could match the 11m-gallon spill from the oil tanker Exxon Valdez off Alaska in 1989.
The oil slick currently has a circumference of about 600 miles (970km) and covers about 28,600 sq miles (74,100 sq km). Its leading edge is now only 20 miles (32km) east of the mouth of the Mississippi. The first of the leaks causing it were found on Saturday, four days after the Deepwater Horizon platform, to which the pipe was attached, exploded and sank.
Eleven workers are missing and presumed dead after the worst oil rig disaster in almost a decade.