A man has been detained for three days for smoking in a Metro station, the first person in Shanghai to be held for violating tough new no-smoking laws,?Shanghai police said yesterday.

The man, surnamed Chen, was found smoking near a ventilation shaft along Line 3 on March 23, police said.

Metro police said his behavior "put subway safety in jeopardy." Usually individual offenders are fined.

A cleaner first detected Chen smoking on Line 3's Hongkou Football Stadium Station, an elevated station, about 2:15pm, police said.

Police arrived shortly after and Chen threw the cigarette butt on the ground.

Chen, 49, was taken to a police station for questioning. He told police he knew that smoking is banned in Metro stations and on subway trains.

Chen climbed a safety barrier and hid near the ventilation shaft and track to avoid being seen.

Police said he was "only 30 centimeters from the facility."

Metro stations are listed as a top level smoking-free zone under the city's smoking control law.

Smoking has been prohibited in public places since the city enacted the ban in March 2010. During the past 12 months, 12 public venues and five individuals were punished for breaking the smoking ban. They were fined a combined 25,400 yuan (US$3,878).

However, many smokers still ignore the ban.

Two fire alerts occurred on the city's Metro network within days last month. One passenger threw a cigarette butt onto a track at Line 3's Jinshajiang Road Station and another cigarette butt started a fire in a garbage bin in a subway station toilet. Both fires were soon put out and no one was injured.

Police said they stopped more than 600 smokers within a week following the fire alerts.

But investigators found some passengers still hide in Metro station toilets to smoke. Smokers also are more likely to light up at elevated Metro stations compared to underground ones, police said.

Meanwhile, police said they seized more than 12,000 dangerous items from 520 checkpoints at Metro stations this year.