The search is continuing for a Malaysia Airlines plane that has been missing for more than 24 hours.
Marine rescue teams worked through the night to search the sea south of Vietnam, while the aerial mission resumed on Sunday morning.
Flight MH370 disappeared en route to Beijing from Kuala Lumpur, with 239 people on board.
At a news briefing in Kuala Lumpur on Sunday morning, officials said there had been no sign of any wreckage.
"The rescue operations continue... and we have to report that we have not been able to locate anything," said Azharuddin Abdul Rahman, a representative of Malaysia's civil aviation authority.
"There is nothing to report at this juncture."
The passengers were of 14 different nationalities. Two-thirds were from China, while others were from elsewhere in Asia, North America and Europe.
'Pray for flight'
It has been reported that two passengers who were listed on the plane's manifest - an Italian and an Austrian - were not actually on the flight.
They both reportedly had their passports stolen in Thailand years ago.
Asked whether terrorism was suspected as a reason for the plane's disappearance, Malaysian Prime Minister Najib Razak said: "We are looking at all possibilities, but it is too early to make any conclusive remarks."
In a statement, the airline urged "all Malaysians and people around the world to pray for flight MH370".
The plane vanished at 17:30 GMT Friday (01:30 local time Saturday).
It reportedly went off the radar south of Vietnam.
According to Malaysia Airlines, it last had contact with air traffic controllers 120 nautical miles off the east coast of the Malaysian town of Kota Bharu.
Distraught relatives and loved ones of those on board are being given assistance at both the arrival and departure airports.
Many have expressed anger at the lack of information.
"They should have told us something before now," a visibly distressed man in his thirties told AFP news agency at a hotel in Beijing where relatives are waiting.
In Kuala Lumpur, Hamid Ramlan, a 56-year-old police officer, said his daughter and son-in-law had been on the flight for an intended holiday in Beijing.
"My wife is crying," he said. "Everyone is sad. My house has become a place of mourning. This is Allah's will. We have to accept it."
'Unity of efforts'
The aerial search was suspended overnight but resumed on Sunday morning.
Malaysia and Vietnam have both sent planes and naval vessels to look for the missing flight.
The US is sending the USS Pinckney, an Arleigh Burke-class guided-missile destroyer, which could be in the area within 24 hours.
Territorial disputes over the South China Sea were set aside temporarily as China dispatched two maritime rescue ships and the Philippines deployed three air force planes and three navy patrol ships.
Singapore is also involved, while Vietnam sent aircraft and ships and asked fishermen in the area to report any suspected sign of the missing plane.
"In times of emergencies like this, we have to show unity of efforts that transcends boundaries and issues," said Lt Gen Roy Deveraturda, commander of the Philippine military's Western Command.
Texas firm Freescale Semiconductor says 20 of its Malaysian and Chinese employees were on the flight, according to a statement on its website.
Vietnam's air force earlier said it had spotted two possible oil slicks 190km (118 miles) from Malaysia, but there is no confirmation they are connected with the plane's disappearance.
Malaysia's national carrier is one of Asia's largest, flying nearly 37,000 passengers daily to some 80 destinations worldwide.
The route between Kuala Lumpur and Beijing has become more and more popular as Malaysia and China increase trade, says the BBC's Jennifer Pak in Kuala Lumpur.
The Boeing 777 had not had a fatal crash in its 20-year history until an Asiana plane came down at San Francisco airport in July of last year.
Three teenage girls from China died in that incident.
Aviation expert David Learmount told the BBC that passenger planes today "are incredibly reliable and you do not get some sudden structural failure in flight - it just doesn't happen".