Beijing police are patrolling the city's subways and trains to stop people wearing face masks, strange costumes and forming flash mobs, warning commuters that such actions could jeopardize public safety by causing stampedes.
State news agency Xinhua said law enforcement teams, which started the patrols on May 1, and have encountered 83 cases of "improper behavior", including hawking, begging and the distribution of advertising flyers.
Costumes and masks are likely to attract the attention of other passengers, Xinhua quoted Liang Jianwei, vice head of the Beijing municipal traffic administration corps, as saying.
"When a lot of people stop to watch, the risk of stampedes increases," Liang said.
Passengers should avoid forming flash mobs, the article quoted Liang as saying.
"Although such behavior is not banned by law, passengers should not be too wilful," Liang said.
Police will warn against "problematic behavior" when they come across it, Liang said.
Last October, state media cited Beijing police as saying that people face arrest for wearing Halloween fancy dress on the subway as it may cause crowds to gather and create "trouble".