Hong Kong police have arrested three visitors from mainland China in a crackdown on a syndicate that stole credit cards from passengers on flights to the city, then made purchases through stores in Vietnam.

A source familiar with the case said the syndicate, which used a hotel room near Hong Kong International Airport as its operations center, may have pocketed millions of Hong Kong dollars in the past three months.

Senior Inspector Wong Yuen-yan of the Sham Shui Po District Crime Squad revealed details of the operation on Friday, saying officers discovered 42 receipts in the hotel room from November 12 or 13, with card transactions worth 360 ​millions of Vietnamese dong ($110,000). ).

A source familiar with the case said police began investigating the syndicate about five weeks ago after learning of its activities on flights to Hong Kong from Asian countries such as India, the Philippines, Malaysia and Vietnam.

Officers identified a 34-year-old man, believed to be a key member of the syndicate, who had rented a room near the airport since August to use as an operations center, the source said.

The man held a return travel permit that allows mainland Chinese residents to visit Hong Kong, and investigations suggested he had made several visits to the city and stayed at the same hotel near the airport over the past three months.