Twenty people have been arrested on suspicion of money laundering, fraud and wasting police resources in cases involving more than HK$2 million, the police said on Wednesday.

In the most serious case, a 19-year-old tertiary student allegedly swindled five people out of more than HK$1.5 million between June and December after accusing them of committing economic crimes on the mainland.

Chief Inspector Cheung Wai-shan said the suspect posed as a secret mainland agent and showed up in person to win credibility with victims.

“To gain their trust, the suspect would first claim to be a secret agent and use coded messages to identify himself to victims," she said.

"These codes, or strings of numbers, would be provided when the suspect met up with victims.

“The suspect would also show the victims a confidentiality order, which appeared to be issued by the mainland's Public Security Bureau. The order would have the victims’ names printed on it to make it look more credible.”

Senior inspector Wong Wai-ting reminded the public that mainland and overseas officers would not be able to enforce their laws within Hong Kong.

She urged people to call the police’s anti-fraud hotline 18222 if they suspect they are being scammed.