The Guangzhou authorities now require sauna clients to show identification and register personal information to try to limit China's booming sex trade, the report said.

The regulation, which came into force on Monday, also aims to prevent criminal suspects from hiding out.

Many massage parlours and saunas in China are fronts for brothels.

'Some of these health centres have become dens of iniquity in past years owing to an absence of efficient supervision and management,' Mr He Jing, deputy director of the city's security bureau, was quoted as saying.

The rule affects those going to massage parlours and saunas from 1am to 8am.

Investigators will be regularly dispatched to enforce the rule, and penalties will range from warnings to revocation of business licences.

Proprietors said the new regulation would affect business, while customers complained it infringed on their privacy, China Daily said.

But others like white-collar worker Li Hongwei said the regulation would help to crack down on the sex trade.

'Many entertainment venues in Guangzhou have recently become hotbeds of vice,' she said.

ASSOCIATED PRESS