Customs officers have arrested four people suspected of laundering around HK$2.6 billion over some 18 months from August, 2023.

Officers said on Tuesday that based on intelligence, they arrested three men and a woman, aged 25 to 56, in recent weeks.

The four are suspected of setting up some 50 bank accounts under three shell companies, with about 6,000 "suspicious transactions" identified.

Michael Ng, an investigator from the department's financial investigation bureau, said the money went in and out of bank accounts of other firms, including some reported to be involved in the seafood and watch businesses.

"None of these transactions bear any relation to the suspects' three companies, which makes little sense," Ng told reporters at a briefing.

"Also, the substantial sums going in and out of the bank accounts far exceed their declared taxable income. These incongruities further heightens the suspicion surrounding these transactions."

Officers seized a number of mobile phones, computers and bank cards in the operation, and froze around HK$2.5 million worth of assets under the suspects' names.

All four were released on bail pending further investigation.