Fifteen years ago, Shenzhen was a rural backwater. Today it is big and ugly and soulless. China's new rich glide over the rubble of 24-hour construction sites in Mercs and BMWs, while street children and cripples beg fiercely for a small share of the city's conspicuous wealth. Its factories are magnets for tens of thousands of migrants from China's farthest flung provinces. The women among them are often tempted or forced into prostitution.

While most parts of China suffer a chronic shortage of women, Shenzhen's males are outnumbered four to one. Anyone doubting this statistic should go to the South China United Movies Recreation Center near the station. Outside, thousands of girls in their late teens promenade in hot pants or thigh-split skirts for the benefit of male buyers. The trade at the plush Century Plaza Hotel nearby is hardly more subtle. The women in its third-floor bar smoke and chat and throw hopeful glances at Hong Kong businessmen, who enter clutching their cellular phones like phallic totems. Taking one of the girls back to your room can cost up to HK$1000 - or three times the monthly wage of a local factory worker. "To get rich is glorious," declared Deng Xiaoping. Getting rich by getting laid probably wasn't what he had in mind.

In Shenzhen there are no loudly advertised, Patpong-style bars with girls doing inventive things with Coke bottles. But there are well-known red-light districts. The most notorious of these is a ten-minute taxi ride from the city center. Huang Bei Ling means "Yellow Shell Ridge," but such is the area's reputation as a hideaway for Chinese lovers of Hong Kong men that locals have rechristened it "Second Wife Village."

Huang Bei Ling is a rabble of shacks and crumbling cottages linked by dim alleyways where rats scarper over trickling lanes of sewage. Frequent power cuts cast the village into a mediaeval, candle-lit gloom. Its one erratically paved road is lined with beauty salons, which are ill-disguised fronts for brothels. Inside, girls preen each other between customers, who will pay a small sum for a head massage while negotiating the price of a quickie - usually around HK$250 a trick.

The only thing more prevalent than salons is venereal disease, as the disproportionate number of pharmacies and clinics suggests. Posters warning against STD hang in nearby hotels, while village clinics feature window displays of gruesome Polaroids illustrating a range of diseases, including AIDS. "There's a lot of sexual disease here because Shenzhen's a very open place," says one doctor with calculated innuendo. "It offers lots of amenities."

The Chinese authorities do make periodic sweeps. One campaign in Guangdong province last year netted over 100,000 pimps and hookers. On the other side of the border, a Hong Kong lawmaker recently tried to introduce a law banning men from keeping mistresses. He failed, but the move spotlighted what many in the colony fear is a latter-day revival of the ancient system of concubinage. Concubines were banned when the People's Republic was founded in 1949 and prostitution is still officially one of the "Seven Evils."

Not that you'd notice in Shenzhen, which has the lawless atmosphere of a border town. I joined the happy crowd which clogged one main road to watch a young punk batter the windows of a taxi which had grazed his motorbike. Rows like these are a modern form of Chinese street theater. The driver spent 20 long minutes locked inside his cab, radioing frantically for help, until a lone policeman arrived to defuse the situation.

Shenzhen's police have more profitable tasks to occupy them than maintaining law and order. In the new China, few people make big bucks without paying off or cutting in venal officials, and the sex industry is no exception. I had dinner with a former Huang Bei Ling cop, who now runs a village beauty salon. With him was Hui, one of his girls. He said she was 18 but she looked much younger, partly because of her inexpertly applied rouge and eyeliner, partly because she seemed so nervous.

Hui picked silently at a plate of eel as her boss talked about Huang Bei Ling. It had long harbored pimps, hookers, drug dealers and gangsters, he said. He explained how local gangs and Hong Kong's Triads collude to smuggle teenage Chinese women into the colony, often against their will. One girl who refused to have sex for money was stripped and locked in a Hong Kong hotel room; she escaped and was later found wandering naked through the streets. Then the cop, aged in his mid-twenties, talked about himself. "In 10 years' time," he predicted, "I'll be a millionaire."

It was impossible to tell whether Hui was as optimistic about her future - the cop answered any questions that were put to her. She left home at 14 and arrived, helpless and terrified, in the nearby city of Dongduan. She worked in factories and karaoke bars there before coming to the Huang Bei Ling salon a few months ago. I asked her if she liked it there. She glanced at her boss. He nodded. "Of course I like Shenzhen," she replied with a tight smile. "Everyone likes Shenzhen."