Beijing is stepping up security checks at subway stations after a series of deadly attacks and before next month's anniversary of the Tiananmen Square crackdown.
The new procedures in China's capital have added as much as an hour to residents' commutes in the notoriously crowded city of 20 million people, with queues outside some subway stations snaking dozens of metres long at rush hour.
Beijing already has hundreds of X-ray machines and security staff stationed at subway stations to check passengers' personal belongings, part of a series of security measures taken ahead of the 2008 Olympic Games.
But the new measures, in force at many subway stations, require passengers to undergo full-body security checks.
Armed police are also being dispatched throughout the city, part of "a three-tier patrol protocol that covers the skies, subways and streets", the state-run China Daily newspaper said Wednesday.
June 4 marks 25 years since the 1989 Tiananmen Square crackdown on pro-democracy protesters, one of China's most politically sensitive anniversaries, and authorities routinely clamp down on any attempts publicly to commemorate it.
China has also been grappling with a spate of violent attacks targeting civilians, which Beijing has blamed on separatists from the far-western region of Xinjiang.
Last week five people killed 39 people and wounded more than 90 at a market in Xinjiang's regional capital Urumqi.
In March knifemen killed 29 people and wounded 143 at a railway station in the southwestern city of Kunming, an incident dubbed "China's 9/11" by state media. (AFP)