Beijing has had smoking bans in place since as far back as the 1990s, and stepped up the campaign before the 2008 Olympics, but the bans have always been weakly enforced.
A Xinhua reporter spotted people smoking indoors in a downtown hospital on Monday.
"I hope the government's momentum to curb smoking can last this time," said someone with the screen name "@skywalker" on microblog Sina Weibo. "Just don't let this ban become another barely-enforced policy nobody remembers after six months."
At a bus stop during the morning rush hour, a volunteer asked scores of people to finish smoking elsewhere before lining up.
"Most stub out their cigarettes at our request but that's the most we can do," the volunteer said. "We are not authorized to fine those who refuse to obey the ban."
The World Health Organization (WHO) suggested mobilizing the public to help enforce the ban.
"If you see someone smoking in a restaurant, tell them to stop! Talk to the manager or owner, or call the national health hotline 12320 to complain," said WHO China Representative Bernhard Schwartlander.
China signed the WHO Framework Convention on Tobacco Control (FCTC) in 2003.
"Beijing's ban on smoking indoors is consistent with China's commitment to the FCTC of protecting the health of non-smokers through enhanced legal support," said Wang Qingbin, a professor with China University of Political Science and Law who helped draft the new smoking ban.
The new ban also serves as a test case for a similar move nationwide. Draft legislation for a national ban has been published to solicit public opinions.
In April, China's top legislature adopted an amendment to the Advertisement Law, banning tobacco advertising in mass media, in public places, public vehicles and outdoors.
China also raised consumption tax on cigarettes at the wholesale level on May 10, a move expected to cut cigarette consumption by 4 to 5 percent and add 100 billion yuan to annual tax revenue.
Data from local price monitoring departments across the country shows the tax rise has largely been passed on to consumers. Cigarettes priced under 20 yuan per pack have seen a price hike of between 0.5 and one yuan. Those priced above 20 yuan have generally been subject to a price rise of around two yuan.
Angela Pratta, who leads the WHO's Tobacco Free Initiative in China, has urged the government to lead by example in enforcing the ban.
"Strong enforcement is critical to ensuring the effectiveness of smoke-free laws, so too is leadership. Senior officials and leaders in government offices need to lead the way by setting an example and supporting enforcement efforts," Pratta said.
