In another initiative, women prisoners will receive training as domestic helpers.

'We've been running smoking-cessation programmes since 2005, but we have not been able to measure its success because once the inmates leave, we don't know if they take up smoking again or not,' said Sin Yat-kin, assistant commissioner of operations in the Correctional Services Department.

Mr Sin said more than 100 inmates, as well as several members of prison staff, had joined courses run by prison nurses trained by the Tobacco Control Office.

Although prisons have been given a permanent exemption from anti-smoking laws introduced on January 1, Mr Sin said steps had been taken to ensure there were smoke-free zones in all prisons.

Smoking booths have been installed in some prisons, but because just 3 per cent of the 9,194 incarcerated male prisoners are non-smokers, small specially designated smoking rooms are unworkable.

'In the men's prisons, for example, we have installed ventilation systems in dining rooms, so parts of the room can be used by smokers, but we have areas that are smoke-free,' Mr Sin said.

He said one prisoner had been disciplined for lighting up in a no-smoking area since January 1.

At Chi Ma Wan women's prison, dealing with smokers is easier, as just 34 per cent of the 433 inmates smoke. In general, about 30 per cent of women prisoners are smokers. The prison's superintendent, Sylvia Chung Chi-lan, said toilets attached to the dining room and dormitories were designated as smoking areas.

Another initiative by prison bosses to help rehabilitate inmates was the introduction last month of a domestic helper training course at Chi Sun women's prison on Lantau, which houses 354 prisoners.

Organised jointly with the Society of Rehabilitation and Crime Prevention (SRCP), the programme aims to provide inmates with a certificate and enough experience making beds, cleaning kitchens and cooking food to find jobs as domestic helpers upon release. So far, 20 women have joined the course.

Jim Fung, of the SRCP, hoped that potential employers would give former inmates a chance.

Meanwhile, women's prisons remain overcrowded, with 2,278 women cramming into jails that were built to hold 2,009.

The Correctional Services Department is regrouping its penal institutions, swapping the young male offenders' Lai King Training Centre with the overcrowded young female offenders' Tai Tam Gap Correctional Institution.

Over the past 10 years, the number of prisoners has fallen, Mr Sin said, mostly due to a drop in arrests of mainland illegal immigrants.