Shanghai will ramp up security and tighten safety checks in the city's metro system, and anyone who refuses to undergo a security check or creates a public disturbance may face criminal detention.

Shanghai public security authorities recently made it clear that refusing security checks at the city's metro network or disturbing public order is a crime, and violators will be punished according to the public management law.

In the past, only those who carried forbidden objects on the subway were punished.

"We will have stricter security checks at the metro stations, and this is very important and necessary for ensuring the safety and the stable operation of metro transportation," said Song Youguo, deputy head of the Shanghai metro police.

In the first four months of the year, Shanghai's metro police have found 165,000 firecrackers, 350 liters of paint, 1,900 use-controlled knives and 88 replica guns during routine security checks at metro stations.

In order to ensure public security, all large bags and luggage must go through an electronic security scanner, while smaller bags will be checked based on the subway staff's judgment, Shanghai public security authorities said.

"Metro security staff will make the judgment and decide which bags should go through the checks. People who refuse to comply with the security checks or behave violently against staff will face punishment, including criminal detention," Song said.

Shanghai authorities also released a more-detailed list of forbidden objects, with flammable items such as phosphorus now included.

Police said the number of crimes on the subway — including obstructing public order, assaulting metro staff and carrying forbidden objects — continues to rise. This year, 10 people have been charged with such offenses, and one of them was detained.

On March 19, a 46-year-old man surnamed Tang was detained after trying to ride the subway with two kitchen knives in his backpack. During the police investigation, the man admitted that he had planned to kill his ex-girlfriend.

In addition to the security checks before entering the underground network, metro police have also carried out security checks and checked the identities of passengers at some key stations during peak times. Official said such checks will become common.

Police also said they will have security checks in the subway carriages.

Shanghai has 14 metro lines with 538 km of track and 329 metro stations. The daily number of passengers is 7,500,000, and on April 4 even reached 9,110,000.

"Security checks do work when it comes to ensuring public safety, though it may cost passengers some time," said a man surnamed Liu.

"I hope the security checks are beneficial. Sometimes, I see some passengers carrying obviously restricted items on the train, so I think the metro staff failed to do their job."

Shanghai metro police said they will help metro staff improve their work and will keep a close eye on them. Employees who fail to do their duties will face dismissal.

This year, 17 subway employees have been dismissed for neglecting their duties, officials said.