The world's biggest offshore oil rig, hit by blasts that apparently killed 10 people, may sink in the next two days, the rig's Brazilian owners said on Friday, raising fears of environmental damage. "Petrobras is in mourning," he said. So far one person has been confirmed dead after three powerful blasts, whose cause is unknown, rocked the rig with 175 workers aboard. Off the coast of Rio de Janeiro state, the giant 40-story rig's deck is now dipping into the water. If it sinks and damages shutters of underwater wells, it could cause Brazil's worst environmental catastrophe, according to engineers. Petrobras, which has experienced environmental disasters over the last few years, said it had five ships around the rig able to contain a potential spill.