BEIJING -?Thirteen restaurant chains in Beijing were warned on Tuesday for not adequately enforcing the smoking ban, which was introduced in the capital's indoor public places in 2015.

The restaurant chains, including steamed bun restaurant Qingfeng and Haidilao Hot Pot, each received more than five complaints, though one chain received as many as 48.

Inspectors and volunteers will launch raids from next week, and will hand out punishments if no improvements have been made.

The Beijing municipal government is considering whether to add punished companies and individuals to a credibility blacklist.

Beijing is home to more than four million adult smokers, and rolled out what has been dubbed the "strictest smoking ban in history" on June 1, 2015, prohibiting smoking in indoor public places, the workplace and public transport.

Wang Benjin, deputy head of Beijing Health Inspection Institute, said there has been reduction in indoor smoking. "But restaurants, office buildings and entertainment venues still receive among the most complaints," he said.

According to the Beijing Tobacco Control Association, a total of 7,603 complaints have been received since September last year, with 42 percent against restaurants.

In the past 16 months, 575 companies and 2,300 individuals have been punished for violating the ban.