pbr Rescuers in helicopters and boats have searched the Gulf of Mexico for 11 missing workers after a thunderous explosion rocked a huge oil drilling platform with a pillar of flame.br ppbr Seventeen people were also injured, four of them critically.br ppbr The blast aboard the Deepwater Horizon rig 50 miles off the Louisiana coast could prove to be one of the deadliest offshore drilling accidents in the US of the past half-century.br ppbr The US Coast Guard is holding out hope that the missing workers escaped in one of the platform's lifeboats.br ppbr A column of boiling black smoke rose hundreds of feet over the Gulf of Mexico as fireboats shot streams of water at the blaze.br ppbr The rig's owner 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 is still under investigation.br ppbr Crews were doing routine work before the explosion and there were no signs of trouble. A total of 126 workers were aboard the rig when it blew up.br ppbr The rig was tilting as much as 10 degrees after the blast, but earlier fears that it might topple over appeared unfounded.