Shanghai health authorities have extended smoking bans from public venues to all indoor workplaces as measures to clear the city's air of cigarette smoke by 2011 are ratcheted up.

Part of a three-year campaign to eradicate passive smoking and stage a salubrious World Expo in 2010, the latest initiative will rid all government buildings, offices, schools and hospitals of harmful passive smoke.

"All places with ceilings and at least three walls will be defined as indoor areas where smoking will be strictly prohibited," Li Mingzhu, director of the tobacco control office under the municipal health bureau, had said previously.

"No designated-smoking areas will be allowed in the smoke-free zones," she said. "This is to minimize the impact of second-hand smoking."

Signs heralding the bans will be in place at all restaurants, hotels and other entertainment venues by 2011.

So far, no-smoking areas have already been established in about 300 restaurants and hotels in the city, with a further 6,000 large and medium-sized such venues scheduled to have them in place by next year.

"We encourage people to take action against smoking indoors and to promote a healthy lifestyle in the city," said an official surnamed Jiang, at the Shanghai Patriotic Health Campaign Commission Office.

Research by Fudan University shows about 70 percent of people obey no-smoking signs.

According to government statistics, China is home to some 350 million smokers, 1 million of whom die of smoking-related diseases each year.

In Shanghai, one in four people enjoy a puff.

This has prompted the city to set up about 60 outpatient clinics where those who wish to kick the dangerous habit can receive advice and treatment.

According to health experts, 10 percent of tobacco addicts who seek professional medical advice or treatment succeed in breaking the addiction. An even lower percentage quits, relying on will power alone.

"At first, patients come because of a respiratory disease without knowing that it was caused by smoking," said Pan Jue, a doctor at the Shanghai Zhongshan Hospital.

The doctor said the hospital has seen an increase in the number of smokers going to seek advice and treatment in recent months.

"When we tell them the cause, and that they can only get better by giving up the habit, they are inclined to do so," Pan said.