Officers in Singapore also took part in what was a joint operation targeting cross-border scams and money laundering, with another four people arrested there.
Two of the four detained in Hong Kong have been charged with conspiracy to defraud and are due to appear before a magistrate on Monday, while the other two are still under investigation.
Chief Inspector Fan Wai-ho said at a press conference that the massive haul of sim cards was sent to Southeast Asia for criminals to make scam calls with.
Fan said they believe the scams raked in HK$120 million between 2023 and early this year.
“During the police investigation, we found modem-pool devices were used as remote information centres which can disguise incoming calls from overseas as local calls. The calls would then be transferred to local victims for scamming activities,” he said.
“The police have contacted two local people who had received suspicious calls from scammers pretending to be officials and customer service staff. But fortunately, they were cautious and communicated with their families, so they did not suffer any loss.”