OVER THE GULF OF MEXICO -- It's a hellish scene: Giant sheets of flame racing across the Gulf of Mexico as thick, black smoke billows high into the sky.

But this is no Hollywood movie. It's the real-life plan to be deployed just 20 miles from the Gulf Coast in a last-ditch effort to burn up an oil spill before it can wash ashore and wreak environmental havoc.

Crews on Wednesday afternoon started a test burn to see how the technique would work. Rig operator BP PLC had planned to continue the oil fires after the test, but as night fell no more were lit. The burns are not expected to be done at night, and the Coast Guard said crews could resume work this morning if the weather cooperated.

Crews planned to use hand-held flares to set fire to sections of the massive spill. Crews turned to the plan after being unable to stop a 1,000-barrel-a-day leak at the spot where a deepwater oil platform exploded and sank.

A 500-foot boom was to be used to corral several thousand gallons of the thickest oil, which will be towed to a more remote area, set on fire and allowed to burn for about an hour.

About 42,000 gallons of oil a day are leaking into the Gulf from the blown-out well drilled by the Deepwater Horizon oil rig. Eleven workers are missing and presumed dead; the cause of the explosion has not been determined.

Greg Pollock, head of the oil spill division of the Texas General Land Office, which is providing equipment for crews in the Gulf, said he is not aware of a similar burn ever being done off the U.S. coast. The last time crews with his agency used fire booms to burn oil was a 1995 spill on the San Jacinto River.

"When you can get oil ignited, it is an absolutely effective way of getting rid of a huge percentage of the oil," he said. "I can't overstate how important it is to get the oil off the surface of the water."

The oil has the consistency of thick roofing tar.

When the flames go out, Pollock said, the material that is left resembles a hardened ball of tar that can be removed from the water with nets or skimmers.

"I would say there is little threat to the environment because it won't coat an animal, and because all the volatiles have been consumed, if it gets on a shore it can be simply picked up," he said.

Authorities also said they expect minimal impact on sea turtles and marine mammals in the burn area.

A graphic posted by the Coast Guard and the industry task force fighting the slick showed it covering an area about 100 miles long and 45 miles across at its widest point.

"It's premature to say this is catastrophic. I will say this is very serious," said Coast Guard Rear Adm. Mary Landry.

Earlier Wednesday, Louisiana State Wildlife and Fisheries Secretary Robert Barham told lawmakers that federal government projections show a "high probability" that oil could reach the Pass a Loutre wildlife area Friday night, Breton Sound on Saturday and the Chandeleur Islands on Sunday.