Security checks at Beijing's subway stations have been stepped up to top level as summer passenger flows increase, the city's public security bureau says.

All luggage and handbags must be screened and up to five security guards will be on duty at each entrance.

Station trash bins will be checked every 10 to 15 minutes to guard against a terrorist attack.

Police, firefighters and anti-terror groups will also help to guarantee security on the system by carrying out random security checks.

Thirty passengers have been reported for refusing to undergo security checks on the subway since the start of the year, the bureau says. Another 120 were detained for carrying prohibited goods.