HO CHI MINH CITY – Vietnamese rescue planes have spotted large oil slicks and a column of smoke off its coastline, but it was not clear if they were connected to a missing Malaysia Airlines carrier, a transportation ministry official said on Saturday. The Malaysia Airlines Boeing 777-200ER plane carrying 227 passengers and 12 crew went missing off the Vietnamese coast early on Saturday as it flew from Kuala Lumpur to Beijing and was presumed to have crashed. “Vietnam rescue airplanes saw two oil spills and one smoke column in the area around 150 miles (250 km) west of Tho Chu island, but we can't confirm it's from that Malaysia plane,” Pham Quy Tieu, vice minister of transportation, told Reuters by telephone. “We sent two maritime boats and some military boats there to clarify, each boat with about 20 people. The oil spills are about 15km long. Those boats will be there in about three to four hours.” A large number of planes and ships from several countries are scouring the area where the plane last made contact, about halfway between Malaysia and the southern tip of Vietnam. There were no reports of bad weather and no sign why the Boeing, powered by Rolls-Royce Trent engines, would have vanished from radar screens about an hour after take-off. By nightfall in the region, there were no signs of the plane or any wreckage, some 17 hours after it went missing. “The search and rescue operations will continue as long as necessary,” Malaysian Prime Minister Najib Razak told reporters in Kuala Lumpur. He said 15 air force aircraft, six navy ships and three coast guard vessels had been pressed into service by Malaysia. China, and the Philippines have also sent ships to the region to help. The United States, the Philippines, and Singapore also dispatched military planes to help in the search. China has also put other ships and aircraft on standby, said Transport Minister Yang Chuantang. Vietnamese Admiral Ngo Van Phat later qualified his earlier remarks about a crash site having been identified and told Reuters he was referring to a presumed location beneath the plane's flight path, using information supplied by Malaysia. The plane, aged over 11 years, disappeared without giving a distress signal - a chilling echo of an Air France flight that crashed into the South Atlantic on June 1, 2009, killing all 228 people on board. Search and rescue vessels from the Malaysian maritime enforcement agency reached the area where the plane last made contact at about 4:30 p.m. local time (0830 GMT) but saw no sign of wreckage, a Malaysian Maritime Enforcement Agency said. – Agencies