Police said another swimmer found the woman floating unconscious in shallow water at Tseung Kwan O Swimming Pool and had to alert a lifeguard to her plight.

A 19-year-old guard dived into the water and pulled the woman out. Colleagues carried out mouth-to-mouth resuscitation and heart massage, but she was declared dead 45 minutes later.

Last night, a spokesman for the Leisure and Cultural Services Department gave a different account. He said a lifeguard who was on duty at the lookout post found the woman floating in the 1.2-metre-deep area of the pool - which ranges from 90cm to 1.2 metres - at about 8.47am. Another swimmer in the pool signalled to the lifeguard that the woman might need help.

He said the lifeguard immediately left his post and pulled the woman from the water with the assistance of other lifeguards. They provided first aid while the pool supervisor called for an ambulance. The woman was taken to Tseung Kwan O Hospital at about 9am.

But the head of the lifeguards' union said that because of manpower cuts, the training pool in which the woman drowned was not manned by guards.

The department spokesman said a lifeguard had been on duty at the lookout post of the training pool, as normal, and he went to the rescue of the woman once he spotted that something was wrong. He said the lifeguard on the lookout post was able to see all areas of the pool.

Twenty-two lifeguards were on duty at Tseung Kwan O Swimming Pool yesterday morning. They were deployed to perform lookout-post, patrols and first-aid duties at seven pool facilities, the spokesman said.

The department said a lifeguard on duty who needed to leave his post for the washroom would arrange a temporary replacement before leaving his position.

Police said there were no suspicious circumstances. An autopsy will be carried out.

Asked if human error was a factor, the spokesman said the department would ask for a report from the pool management to see what action was required. It is understood that the woman, a widow surnamed Lee and originally from the mainland, is survived by an 11-year-old daughter.

Alex Kwok Siu-kit, chief executive of the Hong Kong and Kowloon Lifeguards Union, said that since 2004 the number of lifeguards at the complex had dropped from 30 to about 20. 'Insufficient lifeguards could endanger swimmers and may lead to delays in rescuing or giving first-aid treatment to those who need help.'

Mr Kwok said there had not been enough lifeguards since their numbers were slashed by about 400 to around 1,600 several years ago.

He said the union had repeatedly raised concerns about a lack of lifeguards, but the government had ignored the problem.

'Our colleagues are under extra pressure and workload as most public pools have reached maximum occupancy during the free admission scheme.

'Lives are more important than saving money. We appeal to the government to conduct a thorough review of the manpower of lifeguards.'

The union called on the government to increase the number of lifeguards by about 10 per cent.

The department spokesman said there were sufficient lifeguards manning the swimming pool. Its lifeguard establishment was based on the types of swimming facilities, their usage and experience gained from daily operation. Pool staff had conveyed condolences to the family of the dead woman, he added.