While the clock is ticking on the "24-hour golden window" for search and rescue efforts, it cannot be assumed that there are no survivors from the missing Malaysia Airlines flight MH370, says Indonesia-based independent aviation analyst Gerry Soejatman.
"You can't assume that there are no survivors and if there are any, it is absolutely crucial that they are picked up within a day, or the chances of survival drops significantly," AFP quoted him as saying.
The Boeing 777-200 carried 227 passengers and 12 crew members, from 15 nationalities.
They included 153 Chinese nationals, including an infant, and 38 Malaysians.
Malaysia and Vietnam are leading the search for the plane.
Vietnamese authorities said contact with flight MH370 was lost near their airspace, but its exact location and what happened to it remained a mystery 12 hours after it slipped off air-traffic control screens.
Malaysia Airlines said the plane, on an overnight flight from Kuala Lumpur to Beijing, relayed no distress signal, indications of rough weather, or other signs of trouble.
"The plane lost contact near Ca Mau province airspace as it was preparing to transfer to Ho Chi Minh City air traffic control," a statement on the official Vietnamese government website had said.
Ngo denied earlier reports in Vietnamese state media quoting him as saying the plane had actually crashed.
"Thai and Malaysian rescue teams would be better placed to conduct a rescue but Vietnamese navy boats in Phu Quoc island are ready to support any mission if requested," Phat said by telephone.
The Malaysian navy, air force and army have been mobilised to conduct search and rescue operations.
Acting Transport Minister Datuk Seri Hishammuddin Hussein said a C-130 Hercules had also been deployed to assist in locating the missing B777.
Additionally, the military has also deployed vessels and helicopters to assist in the operations.
The Philippines said it was sending three navy patrol boats and a surveillance plane to help efforts.
Contact was lost at 2.40am Malaysian time, about two hours after take-off from Kuala Lumpur International Airport, Malaysia Airlines group chief executive officer Ahmad Jauhari Yahya said.
"Our focus now is to work with emergency responders and authorities and mobilise full support," he told a press conference in Sepang.
"And our thoughts and prayers are with all affected passengers and crew, and their family members."
Screens at Beijing's airport indicated at first that the flight was "delayed", but later updated its status to "cancelled".
The plane is more than 11 years old.
The flight path of the Kuala Lumpur-Beijing route passes over the South China Sea and the Indochinese peninsula before entering southern Chinese airspace.
At Beijing airport where authorities have gathered the passengers' families at a nearby hotel, an AFP journalist saw one woman enter the arrival zone and break down in tears. She was led away by police.
At KLIA, family members looking sombre and distraught trickled into a designated waiting area for loved ones, escorted by authorities.
"They gave us no information so far," said one man, adding that his niece and her husband were on the flight for a one-week holiday in China. Reporters were barred from entering the area.
The Boeing 777 also has a solid safety record, with only a handful of incidents since its introduction in the mid-1990s.
In July 2013, three people died when a Boeing 777-200 operated by South Korea's Asiana Airlines skidded off the runway upon landing at San Francisco's international airport after it clipped a seawall before touching down.
"We're closely monitoring reports on Malaysia flight MH370. Our thoughts are with everyone on board," US-based Boeing said in a statement on its Twitter feed. – March 8, 2014.