A jobless university graduate from Hong Kong was lured to Cambodia with the promise of a high-paying casino post and held against his will when he refused to pay a ransom, police have revealed.

The 22-year-old was one of 20 city residents since January who became trapped in Southeast Asia after they fell for employment or relationship scams.

The force on Thursday said the man in his 20s fell victim to the employment trap in January after returning to the city upon completing his master’s degree overseas.

Details of the incident were revealed as the city’s Security Bureau launched a cross-departmental task force to coordinate the rescue of Hongkongers held captive in the region.

After sending out more than 100 applications, the young jobseeker noticed an advert on Facebook for a croupier position at a casino in Cambodia with a monthly salary of HK$200,000 (US$25,000) plus a bonus, police said.

After being rescued by local police, the university graduate departed Cambodia safely via Phnom Penh International Airport.

Soon after he replied with his contact number, he received a WhatsApp message from the “recruiter” who claimed training, a free air ticket and accommodation would be provided, the force said on its Facebook page.

He accepted the offer two days later and an air ticket and a hotel room for quarantine were booked by the recruiter.

About a week later, he left Hong Kong for Cambodia on January 11. He quarantined in a hotel room for two weeks before being picked up by so-called casino staff.

The man was driven to an unknown location and the car stopped outside a high-rise building, but he saw no sign of a casino.

He was taken to “staff quarters” on the 10th floor and asked to hand over his passport for his visa application, but he was not required to sign an employment contract.

The next day, he was told a job had been arranged for him and he was taken to the 15th floor of the same building.

“When the door opened, he found more than 40 computers on different tables inside the room. He thought it was a cybercafe rather than a casino,” police said.

“There were several mobile phones on each table. Those who worked there seemed to be very busy sending messages on social media and talking on the phone.”

He realised he had been scammed when he was told to impersonate a woman and follow scripts to persuade men to bet on a gambling website or lure them into investment fraud.

When he refused, he was told he would be released only if he could pay US$10,000 in addition to the air ticket fee and hotel charge. He was then detained against his will in a room and guarded by others.

One night, he managed to call his mother in Hong Kong to beg for help. She immediately filed a police report.

“About a week later, police in Cambodia rescued him. He boarded a flight at Phnom Penh International Airport and returned to the city in early February,” a source said.

No ransom was paid, the insider said, and the victim was unhurt in this case.

Police and immigration officers distribute leaflets at Hong Kong International Airport to remind travellers to be wary of overseas scams.

Another victim was a 28-year-old man who was lured to meet his online “lover” in Thailand where he was abducted in mid-July. He was then taken to Myanmar where he was tortured and imprisoned.

He was released and returned to the city earlier this week after his family paid a ransom.

The Security Bureau on Thursday said 12 of the 20 residents who had been held captive in Southeast Asia were now confirmed as safe, with the remaining eight Hongkongers still being held in Myanmar.

The force posted an account of the victim’s ordeal on its Facebook page again on Wednesday night, having first recounted it in mid-July. A scam alert was also issued on Thursday to urge the public to stay vigilant about such employment frauds.