Two people are missing, feared dead, after a fire broke out on an oil rig off the coast of Louisiana, the US coast guard said on Friday.

Four other workers were seriously injured in the fire on the Black Elk Energy rig in the Gulf of Mexico. A total of 11 were taken to hospital.

Reports of the fire immediately recalled the April 2010 blowout of BP's well in the Gulf of Mexico, which killed 11 men and unleashed one of America's worst environmental disasters.

But the Black Elk Facility – unlike BP's Macondo well – was not a drilling rig, and it was not operating in deep water, which means the potential environmental consequences could be relatively slight.

A sheen of oil about 1km long and 200m wide was reported on the Gulf surface, but officials believe it came from residual oil on the platform.

Rescuers were still searching for the two missing workers on Friday night. Four of the injured workers were critically ill. Taslin Alfonzo, spokeswoman for West Jefferson Medical Center in suburban New Orleans, told the Associated Press that four workers had arrived with second- and third-degree burns over much of their bodies.

Lieutenant Commander Solomon Thompson, from coast guard sector New Orleans, said the rig was a production unit used to pump oil to the surface. "There was some construction on board and then the fire may have broken out as a cause of that construction," he said.

A representative for Black Elk Energy, based in Houston, Texas, said that a team was en route to the site to investigate. "We're still collecting information and as soon as we get all that we're going to be releasing a press statement," a spokeswoman for Black Elk said.

According to Black Elk's website, the company is "an ethical and ecological-minded business".

The well, located some 20 miles off of Grand Isle, Louisiana, is believed to be in relatively shallow waters, perhaps 500ft, initial television news reports said.

Both those factors mean that it will be far easier to cap the well if there is an oil leak.

BP reached a plea settlement for the Deepwater Horizon disaster only on Wednesday, accepting guilt in the deaths of the men and agreeing to pay $4.5bn in penalties. It still faces up to $21bn in civil damages.