Vietnam said its search planes spotted oil slicks in the sea near where a Malaysia Airlines jet carrying 239 people mysteriously vanished on Saturday, in the first hint at the aircraft's possible fate.
The announcement came more than 18 hours after flight MH370 slipped off radar screens somewhere between Malaysia's east coast and southern Vietnam, triggering an international search effort.
"Two of our aircraft sighted two oil slicks around 15 to 20 kilometres (10-12 miles) long, running parallel, around 500 metres apart from each other," the army's deputy chief-of-staff, Vo Van Tuan, told state-run VTV.
"We are not certain where these two oil slicks may have come from so we have sent Vietnamese ships to the area."
Air search operations were halted at nightfall, though ships continued searching, the airline said.
"I think the two oil slicks are very likely linked to the missing plane," Vice-Admiral Ngo Van Phat, who is helping to direct the search mission, told AFP.
"However, we have to check carefully once our rescue boats get access to the area," he said, adding the boats were expected to search a wide expanse of sea in darkness.
A senior Malaysia Airlines official told a press conference at a hotel near Beijing Capital International Airport early Sunday that the "search and rescue team has yet to determine the whereabouts of MH370", 24 hours after it disappeared.
The official said Malaysian authorities had "not received any information if the oil slicks have anything to do with the missing plane".
The twin-engine jet had been flying from Kuala Lumpur to Beijing, where anguished relatives were still desperately waiting for news. It was carrying 227 passengers -- including 153 Chinese nationals -- and 12 crew.
- Stolen passports -
Adding to the mystery over the sudden loss of communication with the aircraft, it emerged that two passengers appeared to have been travelling on stolen EU passports.
An Austrian, named in reports as Christian Kozel, had his passport pinched in Thailand in 2012, while Italian Luigi Maraldi, 37, had his stolen last year, also in Thailand, officials and sources said.
Despite their names being on the passenger manifest, neither man was on the flight to Beijing.
Speaking to reporters in Malaysia, Deputy Transport Minister Datuk Aziz Kaprawi said authorities were probing the matter for possible foul play. "The information is still under review," he was quoted as saying by the Malay Mail Online.
In Washington, a US administration official said authorities were aware of the reporting of the two stolen passports.
"We have not determined a nexus to terrorism yet, although it's still very early and that's by no means definitive. We're still tracking the situation," the official said.
At his house in Kuala Lumpur, Hamid Ramlan, a 56-year-old Malaysian police officer, said his daughter and son-in-law were on the flight for an intended holiday in Beijing.
"My wife is crying. Everyone is sad. My house has become a place of mourning," he said. "This is Allah's will. We have to accept it."
MH370 had relayed no distress signal, indications of rough weather, or other signs of trouble, and both Malaysia's national carrier and the Boeing 777-200 model used on the route are known for their solid safety records.
"We are looking at all possibilities but it is too soon to speculate," Malaysian Prime Minister Najib Razak said, when asked whether terrorism could have been a factor.
Authorities would search "for as long as it takes", he said.
The plane's disappearance triggered a search effort involving vessels from several nations with rival maritime claims in the tense South China Sea.
China, Vietnam, Malaysia, the Philippines and Singapore threw vessels and aircraft into the effort, while the United States dispatched a naval destroyer, with two helicopters aboard, and a surveillance plane.
Overlapping claims to the South China Sea, a resource-rich, vital shipping lane, have been a growing source of friction between China and its neighbours.
- Contact lost after takeoff -
Contact with the aircraft was lost at around 1:30 am Malaysian time (1730 GMT Friday), Malaysian authorities said, about an hour after take-off from Kuala Lumpur International Airport.
Initially, authorities had put the last contact time at 2:40 am. The new time suggests the jet disappeared closer to Malaysia than first thought.
If the worst is confirmed, it would be only the second fatal crash ever for the widely used Boeing 777. A 777-200 operated by South Korea's Asiana Airlines skidded off the runway in San Francisco last year, killing three people.
Malaysia Airlines also has suffered few safety incidents. Its worst occurred in 1977, when 100 people perished in a hijacking and subsequent crash in southern Malaysia.
The 153 Chinese passengers aboard the plane included an infant, while 38 Malaysians and seven Indonesians were aboard.
Six Australians, four French nationals, and three Americans including an infant, were also among those listed and the Dutch Foreign Ministry said it believed one Dutch passenger was on the plane.
The pilot had flown for the carrier since 1981, Malaysia Airlines said. The plane was more than 11 years old.
The lack of information sparked fury among pained relatives in Beijing.
"They should have told us something before now," a visibly distressed man in his 30s said at a hotel where passengers' families were asked to gather.
"They are useless," another young man said of the airline. "I don't know why they haven't released any information."
Malaysia Airlines has sent a team of 93 people to China, whose tasks include helping distraught relatives.
A deadly accident would be a huge blow for Malaysia Airlines, which has bled money for years as its struggles to fend off competition from rivals such as fast-growing Malaysia-based AirAsia.
Analysts have blamed poor management, government interference, and union resistance to reform for holding back the airline.