According to Reuters, Vietnamese rescue planes have spotted large oil slicks and a column of smoke off its coastline, but it is not clear if they are connected to the missing Malaysia Airlines carrier.
"Vietnam rescue airplanes saw two oil spills and one smoke column in the area around 150 miles 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."
Earlier today, international aviation authorities denied reports that the plane crashed south of an island off Vietnam.
The plane lost communications over the South China Sea on a flight from Kuala Lumpur to Beijing, almost 24 hours ago.
Vietnamese website VN Express said a Vietnamese search and rescue official reported that signals from the plane were detected about 120 nautical miles (140 miles) south-west of Vietnam's southernmost Ca Mau province.
However, Malaysian transport minister Hishamuddin Hussein said no signs had been found that the flight had crashed.
Search and rescue crews across south east Asia have been scrambling to find the plane, which was was carrying 227 passengers, including two infants, and 12 crew members.
Passengers were from 14 countries, including 152 from China, 38 from Malaysia, six Australians and four Americans. It is believed no Britons were on board.