NEW ORLEANS (AP) — The Coast Guard by sea and air planned to search overnight for 11 workers missing since a thunderous explosion rocked an oil drilling platform that continued to burn late Wednesday, more than a day since it sent a fireball into the night sky. Seventeen people were injured, four critically.

Nearly 100 other workers made it aboard a supply boat and were expected to reach shore by early Thursday. The blast Tuesday night aboard the Deepwater Horizon rig 50 miles off the Louisiana coast could prove to be one of the nation’s deadliest offshore drilling accidents of the past half-century.

The Coast Guard held out hope that the missing workers escaped in one of the platform’s covered lifeboats. Lt. Sue Kerver said the cutters Cobia and Zephyr were in the Gulf searching for survivors along with three Coast Guard aircraft and a civilian helicopter. She said the search would continue overnight.

Authorities could not say when the flames might die out on the 400-by-250-foot rig, which is roughly twice the size of a football field, according the website of rig owner Transocean Ltd. A column of boiling black smoke rose hundreds of feet over the Gulf of Mexico as fireboats shot streams of water at the blaze.

“We’re hoping everyone’s in a life raft,” Coast Guard Senior Chief Petty Officer Mike O’Berry said.

Adrian Rose, vice president of Transocean, said the explosion appeared to be a blowout, in which natural gas or oil forces its way up a well pipe and smashes the equipment. But precisely what went wrong was under investigation.

Crews were doing routine work before the explosion and there were no signs of trouble, Rose said.

A total of 126 workers were aboard the rig when it blew up. The Coast Guard said 17 were taken by air or sea to hospitals with burns, broken legs and smoke inhalation.

Company officials had not identified the missing workers. The Neshoba County Democrat newspaper in Philadelphia, Miss., reported that the county sheriff’s office notified a Sandtown family that a family member was among the missing.

Carrol Moss, 33, of Jayess, Miss., said Transocean notified her about the explosion early Wednesday. Nine hours later, the company said her 37-year-old crane operator husband, Eugene Moss, was safe.

“That was pure freaking hell,” Moss said inside a suburban New Orleans hotel where she awaited his arrival. “To have your kids look at you and say, ‘Mama, my daddy may not come home’.” The Mosses have four children.

One of the deadliest U.S. offshore drilling accidents was in 1964, when a catamaran-type drilling barge operated by Pan American Petroleum Corp. near Eugene Island, about 80 miles off Louisiana in the Gulf of Mexico, suffered a blowout and explosion while drilling a well. Twenty-one crew members died.

Kelly Eugene waited with nine family members for husband Kevin Eugene, 46, a cook on the rig. A catering company operating on the rig notified her he was safe.

“He’s on the boat. That’s all we know. And that’s all we need to know,” she said.

The rig was tilting as much as 10 degrees after the blast, but earlier fears that it might topple over appeared unfounded. Officials said the damage to the environment appeared minimal so far.

The rig, which was under contract to the oil giant BP, was doing exploratory drilling but was not in production, Transocean spokesman Greg Panagos said. Seventy-nine Transocean workers, six BP employees and 41 contract workers were aboard.

Ted Bourgoyne, a retired professor of petroleum engineering at Louisiana State University, said the explosion was probably caused by natural gas or a mixture of oil and gas coming up through the well, combined with some kind of ignition source.

“In almost all of these things, there’s not one thing that happens; it’s a series of things,” Bourgoyne said.

Rose said the crew had drilled the well to its final depth, more than 18,000 feet, and was cementing the steel casing at the time of the explosion.

“They did not have a lot of time to evacuate. This would have happened very rapidly,” he said.

According to Transocean’s website, the Deepwater Horizon was built in 2001 in South Korea and is designed to operate in water up to 8,000 feet deep, drill 5½ miles down, and accommodate a crew of 130. It floats on pontoons and is moored to the sea floor by several large anchors.

The site of the blast is known as the Macondo prospect, in 5,000 feet of water.

Workers typically spend two weeks on the rig at a time, followed by two weeks off. Offshore oil workers typically earn $40,000 to $60,000 a year — more if they have special skills.

Last September, the Deepwater Horizon set a world deepwater record when it drilled down just over 35,000 feet at another BP site in the Gulf of Mexico, Panagos said.

“It’s one of the more advanced rigs out there,” he said. Panagos said a similar rig today would cost $600 million to $700 million to build.

Kelly Eugene said her husband flew to work on the rig, and until Tuesday’s explosion, that was the part of his job that scared her most. Kevin Eugene has worked in the offshore industry about 12 years and had been on the Deepwater Horizon about a month.

Working on offshore oil rigs is a dangerous job but has become safer in recent years thanks to improved training, safety systems and maintenance, said Joe Hurt, regional vice president for the International Association of Drilling Contractors.

Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf, according to the federal Minerals Management Service.

Despite the long wait for word her husband was safe, Moss said she’s not upset and that the company didn’t want to give bad information.

She said her husband has been working in the oil industry most of his life and that even though he tells her it’s safe, she can’t help but worry.

“I’m a wife and a mother. Of course I worry,” she said.

There are 42 rigs either drilling or doing upgrades and maintenance in depths of 1,000 feet or greater in the Gulf of Mexico, according to the agency. They employ an estimated 35,000 people. Transocean has 14 rigs in the Gulf and 140 worldwide.

The deadliest offshore drilling accident took place in 1988, when an Occidental Petroleum platform about 120 miles off Aberdeen, Scotland, was rocked by explosions and fire. A total of 167 men were killed.

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Associated Press Writers Alan Sayre and Mike Kunzelman in New Orleans and Cain Burdeau in Port Fourchon, La., contributed to this report.