PROSTITUTES and karaoke bars in a small Chinese town are luring growing numbers of cashed-up construction workers from the Chek Lap Kok construction site. Once-sleepy Kwai Shan, near Lantau Island, is spinning illicit profits from the thousands of male workers living on ships and in dormitories at the new airport site. Tung Chung police, on western Lantau Island, say they are powerless to stop workers and locals from slipping across the waters in sampans hired from Tai O village. ''It takes about half-an-hour by motorised sampan. It's very close,'' said an officer of the Port and Airport Development Site branch. ''I think they pay corruption money to the Public Security Bureau, because they don't have to go through immigration.'' The ramshackle outpost is home to about 100 to 200 permanent residents, but at weekends it swells dramatically with the influx of male customers. Ethnic Chinese workers from Chek Lap Kok take advantage of the proximity of cheap beer, prostitutes and the nightlife. Workers use the mainland town as a quick escape from weeks of isolation in all-male work teams. Police said the airport workers paid about $100 to $200 for mainland prostitutes at Kwai Shan - cheap compared to Hong Kong prices. Mongkok District senior operations officers said city prices began at $300 to $400 for Hong Kong Chinese and Thai prostitutes. ''The most expensive are the Malaysians - they're about $800,'' he said yesterday. Another officer said the Chek Lap Kok workers would have to travel further and dig deeper to buy sex from Hong Kong karaoke bars. ''If you go to a karaoke bar and buy a girl out it's about $500 to $800. On top of that you'd have to pay the girl $1,500,'' the anti-triad squad officer said. ''Obviously, compared to those figures, it's cheaper at Kwai Shan.'' Tung Chung police expected the tiny Guangdong town to be swarming with visitors this weekend. ''On Fridays they always go to Kwai Shan and enjoy the weekend over there,'' the officer said. ''But it depends on the weather; if it's bad weather they won't go.'' Villagers from Tai O and Mui Wo used the euphemism ''going to wash their hair'' to refer to each sea-borne jaunt by fading sunlight. ''There are some small hotels, karaoke and barber shops - but the barber shops are actually vice establishments,'' the officer said. Kwai Shan is policed by only two PSB officers who appear to turn a blind eye to the goings-on - as long as the weekend visitors are ethnic Chinese. Other potential customers, including the thousands of Filipino and European workers at Chek Lap Kok, would stand out as obvious foreigners. ''It started about two years ago, but there's a lot more now,'' the officer said. ''They book the sampan here [at Tai O] and go to Kwai Shan. They may pay some corruption money to the PSB because they don't need travel papers. ''It's not a very big town. It's just about the size of the main town of Tai O, not the whole town.''