Estimates about the scale and reach of Dongguan's underground sex trade almost beggar belief.
Between 500,000 and 800,000 people - some 10 per cent of Dongguan's migrant population - are in some way employed in the world's oldest profession, according to Hong Kong's South China Morning Post.
An astonishing 300,000 sex workers - known as "technicians" - are thought to ply their trade in thousands of side-street parlours, hotels, spas and karaoke bars.
"Many wives feel anxious whenever their husbands take business trips to Dongguan," the city's former party chief, Liu Zhigeng, admitted in 2009. "It's disgraceful."
Intent on shedding the city's image as China's capital of sleaze, authorities are now going on the offensive.
A slick campaign seeks to recast this grimy manufacturing city as a picturesque cradle of culture.
"Upon coming to Dongguan, the first thing I notice is that the local people's lives are deeply rooted in traditional culture," gushes the voice-over for one PR film, reportedly produced by the Discovery Channel and aired across China. "The city has an inherent charm, warmth and an amalgamation of cultures. Every day, the city manages to excite."
Security forces are also chipping in, trying to push prostitution off Dongguan's streets with a crackdown on a trade that was outlawed following the 1949 communist takeover. Last month, the New Generation sex market on Dongguan's outskirts became the latest red-light district to be raided by the police. The outdoor market - a tatty labyrinth of concrete car garages - now lies abandoned.
"They closed the market last night," complained one local madam, a woman in her 30s wearing a red tracksuit top. "Normally, we could find you two girls for 150 yuan ($29)."
Dongguan's sex trade may now be less visible than before but many thousands of sex workers still operate inside underground venues that are an open secret to many. On the second floor of one of Dongguan's ubiquitous KTV karaoke bars, two hostesses paraded dozens of girls before their visitors. At least one appeared to be under 18. For 300 yuan, the girls were available for a night of drunken karaoke, fuelled with beer, whisky and cigarettes. For 1200 yuan, guests could retreat to their hotel rooms with the girls.
"I'm married and have a 22-month-old son," said a 28-year-old who was starting her third day at the club and gave her name as Luo. "My husband doesn't know I work here, nor do my parents."
Luo said her route into prostitution had begun in the casinos of Macau where she racked up debts of nearly $145,000.
"I will leave this place after I earn 20,000 or 30,000 yuan and I'll probably return to the casino to try and win it back."
A girl from Jiangxi province who gave her name as Tong said a friend had tricked her into swapping a job at a shoe factory for the KTV bar. "I had no idea what business was going on here until I came," said Tong, who claimed she was 19 but appeared no older than 15 or 16.
Across town, in a roadside massage parlour, three girls were perched on a sofa. A small television beamed CCTV images from the second floor where "special massages" were administered.
Ling Ling, who said she was "20-ish", came to Dongguan from a village in Guizhou, China's poorest province, to work at a toy factory. Soon, she decided she could make a better living out of the massage parlour. "I have no choice. I have to support my family," she said.
Local newspapers have celebrated attempts to give Dongguan a much-needed facelift. One micro-blogger, quoted by the Yangcheng Evening News, said the campaign was "a slap in the face to those who bad-mouth Dongguan".
Asked about their city's campaign to eradicate prostitution, the "technicians" shrugged.
"I heard there have been crackdowns recently," said Ling Ling. "But the police haven't bothered us."
