BEIJING  - Beijing on Monday blamed Kuala Lumpur for a lack of information about a vanished Malaysia Airlines flight, as tearful relatives of the 153 Chinese passengers aboard voiced frustration with all sides of the response effort.
Nearly two-thirds of the 239 people aboard Malaysia Airlines (MAS) flight MH370 were from China, and if the loss of the aircraft is confirmed, it would be China's second-worst air disaster in history.
"The Malaysian side attaches importance to the incident with a sincere attitude, but in light of the situation, the Malaysian side needs to step up their efforts," Chinese foreign ministry spokesman Qin Gang told reporters at a regular briefing.
Qin declined to pinpoint any specific areas of the Malaysian response with which Chinese authorities were dissatisfied, noting that "the incident is still under investigation".
But China's state-run media minced no words on Monday, lashing out at Malaysia and its national carrier over their handling of the missing jet, demanding answers despite the early stage of the investigation and calling for a swifter effort.
Officials said two Europeans whose names were on the passenger manifest - who both had their passports stolen in Thailand - were not on board.
"The Malaysian side cannot shirk its responsibilities," the Global Times newspaper, which is close to China's ruling Communist Party, wrote in a scathing editorial. "The initial response from Malaysia was not swift enough. "There are loopholes in the work of Malaysia Airlines and security authorities," it said.
"If it is due to a deadly mechanical breakdown or pilot error, then Malaysia Airlines should take the blame. If this is a terrorist attack, then the security check at the Kuala Lumpur airport and on the flight is questionable."
China itself regularly enforces heavyweight security, while authorities are often secretive about real or alleged incidents. The China Daily newspaper wrote in an editorial that "terrorism cannot be ruled out", with Malaysian and international authorities still at a loss to explain how at least two passengers were able to board with stolen Italian and Austrian passports.  "Who were they and why were they using false passports?" the paper asked.
"The fact that some of the passengers on board were travelling with false passports should serve as a reminder to the whole world that security can never be too tight, at airports in particular, since terrorism, the evil of the world, is still trying to stain human civilisation with the blood of innocent lives," it added.
Malaysia's police chief said Monday that one of the men who used the passports had been identified, after ministers reportedly said they had Asian facial features.
At a Beijing hotel, Malaysian embassy officials were processing visa applications for families wanting to take up an airline's offer to travel to Kuala Lumpur to be closer to the rescue operations.
The disappearance of a Malaysian airliner about an hour into a flight to Beijing is an "unprecedented mystery", the civil aviation chief said on Monday, as a massive air and sea search now in its third day failed to find any trace of the plane or 239 people on board.
Dozens of ships and aircraft from 10 countries scoured the seas around Malaysia and south of Vietnam as questions mounted over possible security lapses and whether a bomb or hijacking attempt could have brought down the Boeing 777-200ER which took off from the Malaysian capital, Kuala Lumpur.
The area of the search would be widened from Tuesday, Azharuddin Abdul Rahman, the head of Malaysia's Civil Aviation Authority, told reporters.
A senior police official told Reuters that people armed with explosives and carrying false identity papers had tried to fly out of Kuala Lumpur in the past, and that current investigations were focused on two passengers who were on the missing plane with stolen passports.