A survey conducted by an environmental group finds that a government ban on smoking in indoor public venues has been completely ignored by half of Beijing's restaurants, a finding that underscores the challenges of controlling tobacco in a country with 300 million smokers.

The Daerwen Nature Quest Agency, a civil environmental group, conducted the five-month survey of 51 mid-range and low-end restaurants in Beijing in May after the smoking ban was enacted by the Ministry of Health.

The survey, results of which were made public Sunday, found that a complete ban on smoking was imposed in only ten restaurants while it was completely ignored by 25 restaurants. The remaining 16 restaurants separated smoking and non-smoking areas.

China is the world's largest cigarette consumer. The country has 300 million smokers, and more than 740 million non-smokers are regularly exposed to second-hand smoke, according to experts' estimates. About 1.2 million people died of smoking-related illnesses each year.

The central government enacted a ban on smoking in indoor public venues, but experts say the ban, which fails to stipulate supervision and punishment, appears toothless and needs to be upgraded to a comprehensive tobacco control law, which would be the country's first such legislation.

The survey also reveals that air quality was equally bad in restaurants that only partially banned smoking.

The concentration of fine particles (PM2.5), a measurement widely used to gauge air quality, was tested 114 ug/m3 in restaurants that did not ban smoking and 103 in restaurants that partially banned smoking. Both rated four times higher a World Health Organization (WHO) guideline on PM2.5 concentration for short-term exposure, the survey said.

Li Qiang, a researcher with China's National Office of Tobacco Control, said second-hand smoke is a main source of indoor fine particle pollutants whose links with cardiac and respiratory diseases have been proved.

He said the survey also shows that a partial smoking ban, such as setting up smoking areas or smoking rooms, was as bad as no ban at all. "Only a complete ban on indoor smoking can markedly reduce the harm," Li said.