They work in hotels, saunas, massage parlours and karaoke bars; an army of 300,000 whose existence is unacknowledged, whose activities are illegal, and whose industry is irresistibly lucrative and impossible to wipe out. Dongguan has become known as the sex capital of China, where shrewd operators - abetted by accommodating officials - have built a prostitution empire that is estimated to contribute 20 to 30 per cent of the service industry's total output. Under orders from the Ministry of Public Security, municipal authorities this month embarked on a high-profile crackdown to rid the city of this stain, which the party chief admitted was 'disgraceful'. But clamping down is not as simple as closing brothels, jailing operators and removing women. When an estimated one in 10 migrant workers - between 500,000 and 800,000 people - are involved in the sex industry, the impact of a major crackdown would be intense, especially in a manufacturing hub that was buffeted harder than almost any other region by the economic downturn. Added to this is the resistive power of vested interests: wealthy operators, corrupt officials and others who profit from the industry. Prostitution was outlawed by the Communist Party after it took power in 1949, but since the opening up began three decades ago, the world's oldest profession made a comeback. Restrictions were relaxed by local authorities, who could either profit from it or who lacked sufficient resources to keep it at bay. In Dongguan, the scale of the industry attracted Beijing's attention. The city was given until the end of this month to get its house in order; otherwise it would be given the worst crime ranking by inspectors from the Central Committee for Comprehensive Management of Public Security. Party chief Liu Zhigeng vowed to eradicate the city's sex industry, and severely punish cadres and police who colluded with operators. 'Many wives feel anxious whenever their husbands take business trips to Dongguan. It's disgraceful,' he said. However, analysts were sceptical about the campaign. 'A real crackdown on prostitution would undoubtedly destroy Dongguan's economy amid global recession, and this raises the fear of political distrust of Guangdong authorities by the central government,' prominent economic and political columnist Jin Xinyi said. 'More than 500,000 people could be unemployed if Dongguan clamped down on all brothels, massage parlours, nightclubs, sex hotels, sauna centres and karaoke bars.' According to a brothel operator who has lived in Dongguan for 30 years, the sex industry is highly developed and run in the same way as legitimate private businesses. Recruiting is standardised, training is provided, and marketing strategies are conceived and executed. A Changping township resident with detailed knowledge of the industry said anti-sex sweeps had come and gone but prostitution had never been eradicated due to government complicity. 'The city has more than 120 top-end luxury hotels and hundreds of other mid-range places that offer illegal sexual services or lease floors to sex operators. Many township cadres are shareholders in these venues and are offered sexual services as bribes,' he said. 'Successful operators ... have been given important positions at local chambers of commerce and are interviewed in newspapers as public figures.' At a press conference this month, police chief Cui Jian complained that he faced huge pressure whenever he tried to raid a brothel - from cadres who would flood into the bureau and plead on behalf of the operators. And proof of the industry's strength came during police sweeps this month. Only low-level brothels were shut down, while luxury establishments with strong backing continued to enjoy good business. On November 9, nearly 2,000 police raided low-end brothels, including around 50 in Changan township, where prostitutes charge 50 to 100 yuan (HK$57-HK$114) for sexual services. But 50 kilometres away, luxury hotels in Changping and Houjie townships were overwhelmed by clients, some of whom had to find other venues as the prostitutes were fully booked. An operator identified as He Yan said her well-backed brothel, 20 metres from Houjie's police bureau, was untouched. On the same night at a mid-range chain hotel in Houjie, operator Liu Qin encouraged clients to pick from one of her 40 prostitutes, saying the venue was protected by cadres and was the safest place in town. Sex operators from mid-range sauna centres and nightclubs said they hoped the crackdown would not last long, and believed the government had no intention of stamping out prostitution. 'A simple calculation shows you how much the industry has contributed to Dongguan,' one operator said. 'The average client spends 500 to 800 yuan per visit, which translates into a huge sum when a city has 300,000 prostitutes.' Clients came from all over East Asia. 'Many are employed in Dongguan as factory managers or are travelling on business,' he said. Ding Yu , a researcher from the School of Sociology and Anthropology at Sun Yat-Sen University who specialises in the region's sex industry, said factory assembly lines were a rich source of sex workers for Dongguan's brothels. 'Rather than being forced or facing harassment, most prostitutes I have talked to are voluntarily working in the industry after quitting sweatshops,' she said. 'They regard it as a normal job and are happy to earn 10 to 20 times more than their previous factory work. 'Migrant workers getting rich quickly by working as prostitutes will definitely encourage others to follow suit. I have seen all the female migrant workers of an entire village working as prostitutes.' Pan Suiming, a professor from Renmin University and one of China's leading experts on prostitution, has for the past decade advocated legalising the sex industry and recognising the right to work as a prostitute. 'China's sweatshops have fostered prostitution because female workers don't have other career opportunities,' Pan said. 'Our surveys showed that 90 per cent of prostitutes tried to find a factory job before working in the sex industry. Many said they were squeezed by sweatshops. Very few prostitutes said they wanted to return to the assembly lines.'