KUALA LUMPUR - A Malaysian aviation official said here late Sunday that chemical test is being done on oil slick found off northeast Malaysian coast to determine whether it came from the missing airliner.

Director General of the Department of Civil Aviation Malaysia Azharuddin Abdul Rahman told a press conference Sunday evening that oil spill had been found near Tok Bali, Kelantan state, but could not confirm whether it came from the disappeared MAS Flight MH370.

"Our work now focus on locating the vanished jet," the official said. But he declined to give more information on a possible terror probe after the authorities disclosed at least two passengers had boarded the airliner with stolen passports.

A large oil slick stretching 100 nautical miles was found near Tok Bali, Kelantan Sunday by Malaysian Maritime Enforcement Agency.

A total of 34 aircraft and 40 ships are now scouring the South China Sea near the Gulf of Thailand for any sign of the whereabouts of the vanished plane and the search area has been expanded from the South China Sea to the Strait of Malacca.

More Chinese warships are joining the international search and rescue operation.

Late Sunday afternoon, Vietnam sent a boat to investigate a " strange object" spotted by a Singapore search plane near Vietnam's Tho Chu island.

The objects were suspected to come from the Boeing 777 aircraft, Vietnamese press reported earlier. But Rahman has ruled out the possibility that they were from the ill-fated jet.

About 40 hours after Flight MH370 lost contact with air traffic control en route to Beijing from Kuala Lumpurk, the whereabouts of the plane with 227 passengers and 12 crew members onboard remained a mystery.

The flight may have changed route and turned back toward Kuala Lumpur, Malaysian military official told a press conference earlier.

It lost contact with the ground at 1:30 a.m. local time Saturday while flying over the South China Sea.

In a statement earlier, Malaysia Airlines said it feared the worst for its vanished flight.

Malaysian Airlines on Sunday promised to provide families of the passengers onboard the airliner MH370 with timely information, travel facilities, accommodation and emotional support and asked for their patience and support.

When flight MH370 is located, a Response Control Center in the area will be activated to support the needs of families, said Ahmad Jauhari Yahya, CEO of the airlines.