Airport authorities across China have strengthened security checks after the foiled hijacking of an aircraft in the Xinjiang Uygur autonomous region on Friday.

Six Uygur people used crutches and "held items suspected to be explosives" - according to a People's Daily report - to try to break into the cockpit 10 minutes after the airplane took off. The crew and other passengers overpowered them.

Many airports including two in Shanghai and one in the provincial capital Changchun of Jilin, said they had implemented third-level security in light of the attacks.

Similar security measures were taken during the 2010 Shanghai Expo and 2008 Beijing Olympics at airports.

The hijacking means passengers in Shanghai are now more likely to be asked to remove shoes and belts and to open carry-on luggage for thorough searches.

"We hope passengers will understand and cooperate with us as the higher standard (of security) could mean longer check-in time," said the official micro blog of Shanghai airports.

In the wake of the hijacking, airport authorities in Changchun examined risk hazards and checked the deployment of security forces onboard and staff licenses on key flights, according to a report on the website of the Civil Aviation Administration of China.

Tighter security was also seen in other airports for flights to Xinjiang.

The airports of Guangzhou and Shenzhen in South China, and Shenyang in Northeast China, were among those that implemented an "exclusive channel" of security checks for flights to Urumqi.

Many people in Shenzhen posted about the security situation on micro blogs reporting that everyone, including people picking up passengers, had been required go through security checks since Saturday.

Zheng Wenpeng, a spokesman for the airport of Zhengzhou in Henan province, said its airport has already reinforced security despite not receiving official documents from higher authorities requiring it to do so.

Security checks at the Urumqi airport?are especially stringent, with people lining up outside the airport building waiting for their turn to enter.

The information office of Hotan airport told China Daily passengers are being advised to arrive at least one and a half hours before departure, and small metal objects including keys should be placed in check-in luggage.

Meanwhile, authorities in Xinjiang labelled the Friday hijack a "terrorist attack".

"It is a serious and violent terrorist attack by means of hijacking an airplane," said a report on the official website, Tianshan, run by publicity authority of the autonomous region.

Two security staff members, two crew members and four passengers were injured when stopping the hijackers, according to the top civil aviation authority and the official website Tianshan.

Although the hijacking was foiled, the public has expressed concern the attackers managed to take their weapons onboard.

Online accounts of the incident by people claiming to be witnesses said passengers were angry about security checks at the Hotan airport, and argued with staff members.

The airport, located 11.5 km away from the seat of Hotan, has only two security channels and one boarding gate.

Witnesses said one suspect attempted to ignite a home-made detonator on board.

Liu Huijun, a first-class passenger on the flight who witnessed the incident, told China Daily on Sunday he helped foil the attack.

"I saw the man was going to light the fuse of a bottle that was as big as a chewing gum bottle," Liu said. "I stood up quickly and knocked the bottle away. With the joint effort, we passengers and crew members overpowered them."

He couldn't recall the color or material of the bottle, as "it happened all of a sudden and the situation was totally a mess".

Liu said he knew little about the security check and refused to comment on the security work of the airport.

Contact the writers at shaowei@chinadaily.com.cn and wanghuazhong@chinadaily.com.cn

Shi Yingying in Shanghai and An Baijie in Zhengzhou contributed to this story.