KUALA LUMPUR, Malaysia -- Vietnamese air force planes spotted two large oil slicks Saturday in the region where a Malaysia Airlines jetliner disappeared, the first sign that the Boeing 777 with 239 people aboard had crashed.
The air force planes were part of a multinational search operation launched after Flight MH370 fell off radar screens less than an hour after taking off from Kuala Lumpur bound for Beijing.
The oil slicks sighted off the southern tip of Vietnam were each between 10 kilometers (6 miles) and 15 kilometers (9 miles) long, the Vietnamese government said in a statement.
There was no immediate confirmation that the slicks were related to the missing plane, but the government said they were consistent with the kind of slick that would be produced by the two fuel tanks of a crashed jetliner.
After the oil was spotted, the air search was suspended for the night and was to resume Sunday morning. A sea search continued, the airline said.
The jet was believed to be flying at cruising altitude when it vanished.
Malaysia Airlines CEO Ahmad Jauhari Yahya said there was no indication the pilots had sent a distress signal, suggesting that whatever trouble befell the plane happened quickly, perhaps in a sudden catastrophe.
The plane was last inspected 10 days ago and was "in proper condition," Ignatius Ong, CEO of Malaysia Airlines subsidiary Firefly airlines, said at a news conference.
Two-thirds of the jet's passengers were from China. The rest were from elsewhere in Asia, North America and Europe.
Asked whether terrorism was suspected, Malaysian Prime Minister Najib Razak said authorities were "looking at all possibilities, but it is too early to make any conclusive remarks.”
Contributing to fears of foul play was word from foreign ministries in Italy and Austria that the names of two citizens listed on the flight's manifest matched the names on two passports reported stolen in Thailand.
Italy's Foreign Ministry said an Italian man who was listed as being a passenger, Luigi Maraldi, was traveling in Thailand and was not aboard the plane. It said he reported his passport stolen last August.
Austria's Foreign Ministry confirmed that a name listed on the manifest matched an Austrian passport reported stolen two years ago in Thailand. It said the Austrian was not on the plane, but would not confirm the person's identity.
At Beijing's airport, authorities posted a notice asking relatives and friends of passengers to gather at a nearby hotel to await further information. A woman aboard a shuttle bus wept, saying on a mobile phone, "They want us to go to the hotel. It cannot be good.”
Passengers' loved ones were escorted into a private area at the hotel, but reporters were kept away. A man in a gray hooded sweatshirt later stormed out complaining about a lack of information. The man, who said he was a Beijing resident but declined to give his name, said he was anxious because his mother was aboard the flight with a tourist group.
"We have been waiting for hours and there is still no verification," he said.
In Kuala Lumpur, family members gathered at the airport, but were also kept away from reporters.
The plane was last seen on radar at 1:30 a.m. (1730 GMT Friday) above the waters where the South China Sea meets the Gulf of Thailand, authorities in Malaysia and Vietnam said.
Lai Xuan Thanh, director of Vietnam's civil aviation authority, said air traffic control in the country never made contact with the plane.
The plane "lost all contact and radar signal one minute before it entered Vietnam's air traffic control," Lt. Gen. Vo Van Tuan, deputy chief of staff of the Vietnamese army, said in a statement.
The South China Sea is a tense region with competing territorial claims that have led to several low-level conflicts, particularly between China and the Philippines. That antipathy briefly faded Saturday as China, the Philippines, Vietnam, Singapore and Malaysia all sent ships and planes to the region.
Najib said Malaysia had dispatched 15 planes and nine ships to the area. The U.S. Navy was sending a warship and a surveillance plane, while Singapore said it would send a submarine and a plane. China and Vietnam also were sending aircraft to help in the search.
Finding the wreckage of aircraft that go down over ocean waters can often take days. Locating and then recovering the flight data recorders can take months or even years.
The plane was carrying 227 passengers and 12 crew members, the airline said. It said there were 152 passengers from China, 38 from Malaysia, seven from Indonesia, six from Australia, five from India, three from the U.S., and others from Indonesia, France, New Zealand, Canada, Ukraine, Russia, Taiwan and the Netherlands.
Malaysia Airlines has a good safety record, as does the 777, which had not had a fatal crash in its 19-year history until an Asiana Airlines plane crashed last July in San Francisco, killing three passengers, all teenagers from China.
Airliner "black boxes" -- the flight data and cockpit voice recorders -- are equipped with "pingers" that emit ultrasonic signals that can be detected underwater. Under good conditions, the signals can be detected from several hundred miles away, said John Goglia, a former member of the U.S. National Transportation Safety Board. If the boxes are trapped inside the wreckage, the sound may not travel as far, he said. If the boxes are at the bottom of an underwater trench, that also hinders how far the sound can travel. The signals also weaken over time.
Air France Flight 447, with 228 people on board, disappeared over the Atlantic Ocean en route from Rio de Janeiro to Paris on June 1, 2009. Some wreckage and bodies were recovered over the next two weeks, but it took nearly two years for the main wreckage of the Airbus 330 and its black boxes to be located and recovered.
Malaysia Airlines said the 53-year-old pilot of Flight MH370, Zaharie Ahmad Shah, has more than 18,000 flying hours and has been flying for the airline since 1981. The first officer, 27-year-old Fariq Hamid, has about 2,800 hours of experience and has flown for the airline since 2007.
A wingtip on the same Malaysian Airlines Boeing 777-200 broke off Aug. 9, 2012, as it was taxiing at Pudong International Airport outside Shanghai. The wingtip collided with the tail of a China Eastern Airlines A340 plane. No one was injured.
Malaysia Airlines' last fatal incident was in 1995, when one its planes crashed near the Malaysian city of Tawau, killing 34 people. The deadliest crash in its history occurred in 1977, when a domestic Malaysian flight crashed after being hijacked, killing 100 people.
In August 2005, a Malaysian Airlines 777 flying from Perth, Australia, to Kuala Lumpur suddenly shot up 900 meters (3,000 feet) before the pilot disengaged the autopilot and landed safely. The plane's software had incorrectly measured speed and acceleration, and the software was quickly updated on planes around the world.
Malaysia Airlines has 15 Boeing 777-200s in its fleet of about 100 planes.
Chris Brummitt reported from Hanoi, Vietnam.
Associated Press journalists Didi Tang and Aritz Parra in Beijing; Stephen Wright in Bangkok; Colleen Barry in Milan; George Jahn in Vienna; Jim Gomez and Oliver Teves in Manila, Philippines; Joan Lowy in Washington; and Scott Mayerowitz in New York also contributed this report.