From Sky News:
"The two parallel slicks - both between 10 miles (16km) and 12 miles (19km) long and 500 metres apart - were seen by two Vietnamese air force jets off the south coast of Vietnam."
"A Vietnamese government statement said they were consistent with the kind of spills caused by fuel from a crashed airliner.
Rescue boats are being sent to the area from the nearby island of Phu Quoc to look for survivors."
Malaysia Airlines Plane 'Crashes Near Vietnam'