An Iranian oil tanker that sank in flames off the east coast of China is thought to be leaking heavy bunker fuel, raising fears of an environmental disaster. Heavy oil is used in ships' engines, and is difficult to remove from the sea. The cargo of lighter oil may also be leaking, with slicks spotted exceeding some 77 square miles. The Iranian tanker had been adrift and ablaze after crashing into a freight ship on January sixth. The crew of 30 Iranians and two Bangladeshis are believed to have been killed. It's not immediately clear where any oil could wash up, or the extent of damage it could cause. Experts say that to avoid further damage, the best option now is to salvage the ship. Noting that the process will present "huge risks and difficulties" - and that the remaining light oil could catch fire again.