China's state-run media on Monday lashed out at Malaysia and its national carrier over their handling of the missing passenger jet, calling for a swifter response effort and tightened airport security.
Chinese President Xi Jinping and US President Barack Obama meanwhile spoke by telephone Monday, with Obama offering his sympathy and saying the US was willing to work "comprehensively" with China on the rescue effort, Beijing's foreign ministry said.
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.
Investigations have been launched into suspect passengers after 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 the ruling Chinese 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."
- Terrorism fears -
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 Home Minister Zahid Hamidi reportedly said Sunday that the two passengers using stolen passports appeared to be ethnically Asian.
"I am still puzzled how come (immigration officers) cannot think: an Italian and Austrian but with Asian facial features," he was quoted as saying by Malaysia's national news agency Bernama.
At a Beijing hotel, Malaysian embassy officials were processing visa applications for families wanting to take up an airline offer to travel to Kuala Lumpur to be closer to the rescue operations.
Scores of relatives made their way into the room, some in groups of five or six, clutching handkerchiefs and wiping away tears from their faces.
Others said they would not go. "There is more we can do here in China," one woman told AFP. "They haven't even found the plane yet."
- Calls for action -
Some have criticised Malaysia Airlines' response and information disclosure, asking the Chinese government to devote "strong attention" to the incident.
Beijing sent a working group to Malaysia Monday, the official Xinhua news agency said, including officials from the foreign, public security and transport ministries, tasked with investigating the incident and helping passengers' family members in Malaysia.
The aircraft's disappearance came one week after a deadly attack at a train station in the southwestern Chinese city of Kunming, in which a group of knife-wielding assailants killed 29 people and wounded 143.
Both Beijing and Washington have condemned the mass stabbing as an act of terror, and Chinese authorities stepped up security checks in the days after the attack, which they blamed on separatists from the restive far western region of Xinjiang.
In his phone call with Obama, Xi said China will maintain "close contact" with the US, according to a Chinese foreign ministry statement.
The Global Times noted that China has the world's greatest number of outbound travellers, with Malaysia a popular destination. A total of nearly 100 million Chinese tourists visited foreign countries last year, up 14 million from the previous year.
"We pay special attention to the security situation of countries where the Chinese people are keen to travel," the paper wrote, adding that the incident "must be investigated thoroughly and the crux of problems on the Malaysian side must be found out".