A Malaysia Airlines flight carrying 227 passengers and 12 crew has gone missing over the South China Sea, presumed crashed.
The airline on Saturday said search and rescue teams from countries closest to the missing plane's flight path had been sent to scour a large area near its last known location.
Vietnam said its rescue planes spotted two large oil slicks in the sea and it was sending boats to the area.
"Two of our aircraft sighted two oil slicks around 15 to 20km long, running parallel, around 500 metres apart from each other," the army's deputy chief of staff, Vo Van Tuan, told state-run VTV.
A crash, if confirmed, would mark the United States-built Boeing 777-200ER airliner's deadliest incident since entering service 19 years ago.
Malaysia's flag carrier said flight MH370 disappeared, without giving a distress signal, at 2:40am local time on Saturday (18:40 GMT Friday), about two hours after leaving Kuala Lumpur International Airport. It had been due to arrive in Beijing at 6:30am local time on Saturday (22:30 GMT Friday).
The flight was carrying 154 people from China or Taiwan, 38 Malaysians, seven Indonesians, six Australians and five Indians, the airline said.
There were also three US citizens, four from France, two passengers each from New Zealand, Ukraine, and Canada, and one each from Italy, the Netherlands, Russia and Austria, the airline said in a statement.
However, Foreign Ministry officials in Rome and Vienna later said names of two nationals listed as passengers matched passports reported stolen in Thailand.
The Austrian, whose passport was stolen two years ago, was found safe at home, a ministry spokesman said.
Italian news agency ANSA said Luigi Maraldi called home after hearing reports that an Italian with his name was aboard the plane.
Al Jazeera's Rob McBride, reporting from Beijing, said that it is a very hard situation for the airline as it does not have the visual confirmation that its plane has crashed. "The company does not want to say so until it has confirmation," he said.
Al Jazeera’s Florence Looi, reporting from Kuala Lumpur, said that the search teams concentrate rescue efforts on the area where contact was last made with the aircraft.
"There are more than a dozen Malaysian planes involved in the search and rescue mission and about nine ships from the same country. Singapore and Vietnam are also involved in the mission. And the US is sending two ships," she said.
The airline said it was working with authorities in the search efforts to locate the aircraft.
No distress signal
Ross Aimer, a former pilot with United Airlines, told Al Jazeera it was highly unusual that air traffic control would lose contact with an aircraft without communication from the crew.
"The fact that there was absolutely no distress signal is very disturbing. This is almost unprecedented that we lose an aircraft in such a way … In that area of the world, over Vietnam, there is sporadic radar coverage to begin with," he said.
A report by China's Xinhua news agency said contact was lost with the plane while it was near Vietnamese airspace.
The airline's Kuala Lumpur-Beijing route passes roughly over the Indochinese Peninsula.