Swift Energy and the US Coast Guard are "aggressively attacking" a spill from a previously shut-in Gulf of Mexico wellhead after it was struck by a crew boat, authorities said late on Wednesday.
Well owner Swift Energy has hired a barge to fix the wellhead, which is leaking oil and water at a rate of about 20 barrels (840 gallons) per day, the Coast Guard said in a statement.
About 1800 feet of boom has been laid to contain pollution and two skimmers are working on scene.
"We’ve quickly mobilised boom to contain, skimmers to clean up spilt oil and operations to plug the well are our top priority," Peter Gautier, Captain of the Port for Coast Guard Sector New Orleans, said in a statement.
"Well control operations will start tomorrow morning.”
The "well-control incident" occurred around 19:00 on Tuesday evening in Swift's shallow-water Lake Washington field about nine miles south-west of Port Sulphur, Louisiana, the company said.
"This collision damaged the integrity of the wellhead and resulted in an outflow of water, oil and natural gas," it said in a statement.
A spokesman said he did not know who owns the vessel that allided with the wellhead. The US Coast Guard identified the vessel as the 42-foot crew boat Sea Raider.
The well has been shut in since January 2008. The most recent test of the well, taken shortly before it was shut-in, recorded production levels of 18 barrels per day of oil, three bpd of water and 59,000 cubic feet per day of natural gas.
"At this time, the well appears to be releasing primarily water and a small amount of oil," Swift said in a statement earlier on Wednesday. "A definitive determination of oil volumes is difficult to measure currently due to the high ratio of water production."
An incident command team responded to the incident overnight, Swift said. The team deployed primary containment boom and oil-skimming equipment around the well site.
"Additional containment and skimming equipment is being deployed to protect any nearby marsh lands," Swift said.
No injuries were reported.
Swift said it is working closely with state, federal and local authorities to respond to the incident. The company conducted a flyover of the field on Wednesday "to determine the extent of the impact to the surrounding area".
Swift is in the process of developing a definitive plan and time line to bring the well under control.
The oil spill comes as UK supermajor BP faces trial in New Orleans for negligence in the deadly 2010 Macondo disaster, which led to the worst oil spill in US history.