Mumbai, June 13 :    Mumbai, June 13:  A supertanker, twice as big as an aircraft carrier, sank off the Indian coast early today after a mid-sea explosion split the vessel in two, Coast Guard officials said. The ship had 42 crew on board, 38 of whom were rescued by two merchant vessels nearby. A sea and air search is on for the missing four. Heng San, a 25-year-old large crude carrier, run by Ocean Tankers of Singapore, sank after midnight, 389 nautical miles west of Mangalore. The tanker was empty and bound for the United Arab Emirates, where it was to load cargo. Coast Guard officials said an explosion in one of the cargo tanks blew a hole in the ship, sinking it. The vessel weighed 2,41,000 deadweight tonnes, when fully loaded. The cause of the explosion is not known. But it was so powerful that it blew up the deck and most cargo tanks, gutting and splitting the ship in two. London-based Lloyds Shipping Intelligence said the sinking ship had sent out a distress call, picked up first by the Maritime Rescue Co-Ordination Centre in Norway. It immediately alerted MV Cloverly, a merchant vessel, barely 23 miles from the sinking tanker, which in turn informed MV Aztec, another ship nearby. The two ships together rescued 38 crew members. The Norway centre also alerted the Indian Coast Guard. It contacted a tanker, MT Probabaro, sailing in the area and asked it to join the search. It also alerted naval vessels, which pitched in. Indian naval aircraft joined the search this morning. No bodies were found. A Coast Guard spokesman said they are not sure whether the missing people are alive. The rescued crew members include 30 Chinese, seven South Koreans and a Myanmar national. The captain of the tanker is among those rescued. There wasn't any Indian among the crew, Coast Guard officials said. It is not clear where the rescued crew are being taken. Coast Guard officials said they was no oil-spill as the tanker was empty. A shipping ministry official, however, countered this, saying a supertanker consumes 100 tonnes of fuel a day and might have been carrying 2,000 tonnes of fuel. The tanker's engine fuel might have caused a spill.