The Immigration Department has warned of an emerging people-smuggling tactic in which illegal migrants use genuine Hong Kong passports to travel overseas via the city. The trend coincides with a sharp decline in the use of bogus travel documents - once widely used by people-smugglers - following the introduction of more sophisticated e-passports. The new tactic was detected 96 times last year. Most cases involved mainlanders who impersonated the rightful passport holders to board flights. Fifteen of those cases involved Hong Kong passports. Six of them held genuine e-passports issued by the department after February 2007. 'Some mainland illegal migrants will come to Hong Kong for a stopover using their legitimate passports, usually with a valid visa to Thailand,' Eric Chan Kwok-ki, the department's assistant director for enforcement and litigation, said. 'They check in for the Thailand-bound flight and wait in the airport's transit lounge, where members of smuggling syndicates bring them genuine passports and boarding passes for their real destinations.' The scheme costs each illegal migrant HK$150,000 to HK$300,000. Mr Chan said the syndicate sells the passports to people with faces similar to those in the documents. They help them change their appearance, such as hairstyles and their spectacles, to deceive officers. 'They are trying to take advantage of a perception that Asians look alike in the eyes of Caucasians. But our officers, with professional training, can spot the flaws by talking to the travellers,' he said. Officers approach travellers and check their documents in departure lounges. The syndicates buy genuine passports from Hong Kong residents for between HK$500 and HK$3,000, Mr Chan said. The department's 60-strong anti-illegal migration agency was conducting plain-clothes operations at Chek Lap Kok airport around the clock to tackle the problem, he said. A tactical intelligence group has also been set up under the agency to boost intelligence gathering both in Hong Kong and other jurisdictions. Passengers on 22,873 flights had their identities checked last year, up from 21,538 flights in 2007. Officers do their work in public areas of the airport. A total of 102 Hong Kong residents and a Malaysian visitor - all members of international syndicates - were arrested last year for involvement in people smuggling. Eighteen of them were convicted and sentenced to between 21/2 months and three years in jail. The others are going through judicial assessments or pending trial. The department will focus on stopping impersonation cases in future, seeing it as an inevitable trend following the introduction of more sophisticated biometric e-passports, Mr Chan said. The department has not yet seized any bogus Hong Kong e-passports since they were first issued in 2007, and the number of forged Hong Kong passports found has dropped from 280 in 2002 to 75 last year. Total seizures of false travel documents fell to 1,423 last year, the lowest since 2002. 'It has proved to be too difficult to forge e-passports, which forces the syndicates to turn to impersonation,' Mr Chan said. Last week, a Hong Kong resident and two mainlanders were jailed for conspiring to possess forged Malaysian and Japanese passports, and were sentenced to three years and 20 months in jail, respectively.