The oldest man in the current vice ring case, a 75-year-old, was among five men convicted on Thursday of engaging in commercial sex with a young China girl who was forced to become a prostitute in Singapore.

Three of the four men - Chong Kwong Ann, Tiah Oon Kai and Li Weichao - were each jailed for 12 weeks while Toh Toh Loh was jailed for 11 weeks. The case against the youngest man, 22-year-old Yap Jun Hao was postponed to Oct 11 for mitigation.

Chong, 75, unemployed, and Li, 42, a construction worker, faced two charges each of paying the 17-year-old $60 each time, but the prosecution only proceeded on one charge. Tiah, 66, a bookkeeper, the court heard, did not verify the minor's age.

The court heard that the girl had financial problems due to her late father's debts of about 100,000 yuan (S$21.0000) for his medical treatment. She worked in a hair salon in her hometown Shandong, and was brought to Macau by her employer to work in a casino to earn more money. But as she was underage, she could not get a job in the casino.

She was tricked by the pimp's sister, Tang Huiying, into meeting her brother, Tang Huisheng, 36, in Zhuhai, China. Tang Huisheng drugged her and had sex with her. When she refused, he assaulted her.

The minor tried to escape by leaping out of her fifth-floor room where she was held for more than a week. She was caught by Tang, who together with his sister, beat her up.

Tang, who has claimed trial, brought her to Singapore on May 16. The minor started work as a prostitute in Geylang two days later until her arrest on June 1.