By Anna Driver and Bruce Nichols
HOUSTON (Reuters) - Eleven workers were missing and 17 injured in an explosion at a Transocean oil drilling rig off Louisiana, and crews were fighting the fire 16 hours later, the U.S. Coast Guard said on Wednesday.
An estimated 126 people were aboard the Deepwater Horizon at the time of the explosion, reported about 10 p.m. local time (0300 GMT) Tuesday.
The rig was drilling for BP Plc 42 miles southeast of Venice, Louisiana, near the mouth of the Mississippi River, in Mississippi Canyon block 252, Transocean said.
The rig -- a "semisubmersible" towed to a site and partially sunk on pontoons for drilling stability -- was reported at midday Wednesday to be leaning, and spilling fuel and either oil or drilling fluid from the wellbore, a Coast Guard spokeswoman said.
Five firefighting vessels were trying to control the blaze, the spokeswoman said. Photographs showed flames leaping high in the air and engulfing the rig after the blast.
"Our No. 1 priority is the search and rescue for 11 missing crew members," Coast Guard Petty Officer Elizabeth Bordelon said.
The search area had been extended in case survivors stayed afloat, but were pulled from the immediate scene by ocean currents in the hours after the blast, the spokeswoman said. She could not say how far.
Initial reports were as many as 12 missing, but the Coast Guard counted 98 survivors on two oil service boats and 17 injured, seven critically, who were taken to hospitals. Eleven were still unaccounted for at midday Wednesday, the spokeswoman said.
The Coast Guard deployed helicopters, planes and vessels to look for the missing workers, sent environmental crews to the scene to assess and control any spill and launched a joint investigation with public and private interests into the cause.
A safety zone with a radius of five nautical miles around the crippled vessel was declared to keep traffic in the area at a minimum, but cleanup efforts had not yet been initiated, the spokeswoman said.
"There is a slick, but right now we're focused on search and rescue," she said.
Transocean, based in Zug, Switzerland, is the world's largest offshore drilling contractor.
Shares of Transocean had fallen 2 percent to $89.99 on the New York Stock Exchange by midday.
(Additional reporting by Matt Daily in New York and Janet McGurty in Toronto)