Undercover policewomen posing as karaoke customers arrested six mainland men in Jordan early yesterday on suspicion of offering sexual services. Two policewomen, posing as wealthy customers, went to a restaurant in Shanghai Street that allegedly turns into a nightclub for women after 11pm. The agents paid their bill - more than HK$3,000 - before declaring their identities and making the arrests about 3.30am. Six mainland men, aged between 23 and 33, were apprehended for breaching their condition of stay. One was accused of offering a sex service to one of the policewomen, according to police. During the operation, there were about 10 female customers and 15 local male prostitutes, but none was held for questioning. The eatery, near Tsim Sha Tsui police station, provided Thai dishes between 11am and 11pm but turned into a nightclub for women between 11pm and 5am, police said. 'Clients were approached asking whether they needed company to play drinking games and drink and sing together,' said Senior Inspector Upathamchart S.A. of Tsim Sha Tsui police station. Customers paid male prostitutes HK$500 for drinking and singing, but were charged thousands of dollars for sexual services. Police said it had been operating for about six months, initially offering Thai male prostitutes. Recently mainland male prostitutes were brought in. 'One local male prostitute told us he could earn as much as HK$40,000 a month. We believe its operator could make at least HK$500,000 a month,' a police source said. The operation was mounted after police carried out months-long investigation and surveillance. The two undercover policewomen visited the restaurant several times before yesterday's raid. Last year police arrested 24 suspected male prostitutes in another Thai restaurant in the same district. Prostitution is not illegal in Hong Kong but tourists with travel visas working in Hong Kong break their condition of stay.