China has urged Malaysia to intensify its efforts to find Flight MH370, as frustration at the failure to locate the missing jet threatened to boil over.

“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,” said Qin Gang, a spokesman for the foreign ministry.

The Boeing 777 jet vanished at 1.20am local time on Saturday morning, roughly 40 minutes after taking off from Kuala Lumpur on route to Beijing. The skies were clear and the plane, with more than 150 Chinese on board, sent no distress signal.

It emerged on Monday that five passengers who checked in to fly on the missing airline had not boarded the plane, despite checking in baggage. Malaysia Airlines had removed the baggage once it learned they did not board the plane, in line with standard procedure.

“This happens all the time,” said one aviation expert who asked not to be named. “People get lost in Duty-Free, or in the airport and they just don’t make their flight”.

In Beijing, the friends and relatives of the missing passengers voiced their anger after another long day of waiting in a downtown hotel.

A Malaysian Airlines representative was pelted with water bottles and called a liar at a briefing, while Chinese officials were also greeted with abuse and shouted questions.

“We have almost 100 people working on the case,” said the representative from the Chinese government. “If you are unhappy, you should be unhappy at Malaysia Airlines. The government has no problem with you. The government strongly supports you.”

Asked if the plane had been hijacked, the government official said there was “no sign of any hijacking”.

But in an illustration of the total vacuum of information about Flight MH370, a Malaysian government official said in Kuala Lumpur that a hijacking could also “not be ruled out”.

“To confirm what really happened we need hard evidence, concrete evidence. We need parts of the aircraft to analyse and do forensic study,” said Malaysia’s civil aviation chief, Azharuddin Abdul Rahman.

“We have not found anything that appears to be objects from the aircraft, let alone the aircraft. We will be intensifying our efforts.”

He added that various reports over the past few days of objects sighted in Vietnamese waters had proved to be false leads.

“A number of aircraft spotted an object that looked like the tail, but when we sent ships, we found logs tied together into what looked like a pontoon,” he said.

“For the aircraft to just go missing just like that, there are many theories and many experts who have contributed their knowledge about what has happened. As far as we are concerned we are equally puzzled,” he added.

An analysis of the oil slick found in the location the plane went missing is expected later today, and CCTV footage of the two men who were travelling on the flight with stolen passports will also shortly be released.

Australia, China, Thailand, Indonesia, Singapore, Vietnam, Philippines and the United States have all sent search and rescue ships, helicopters and planes as the hunt broadens for the missing jet.

Additional reporting by Adam Wu

Photo Credit: A woman, believed to be the relative of a passenger onboard Malaysia Airlines flight MH370, cries at the Beijing Capital International Airport. Kim Kyung-Hoon / Reuters