Police on Thursday said they had arrested four people on suspicion of money laundering, freezing HK$70 million in donations that the force claimed could have been spent on paying youngsters to join the city's anti-government protests.
Those arrested, aged between 17 and 50, were members of Spark Alliance HK, which has been raising money to support protesters who get into difficulties.
The group said the donations would go towards paying legal and medical fees, as well as food for protesters.
But acting senior superintendent Chan Wai-kei said police had found some "pretty suspicious" financial activity linked to the group.
"Our police action today was based on suspicious financial transactions conducted by a shell company. In the past six months, we found there were large cash deposits. Pretty suspicious deposits into this shell company which were incommensurate with its business nature," Chan said.
"Furthermore we found that a large amount of money has been used to purchase personal insurance products of which an individual was the beneficiary. Again, it is incommensurate with his personal income."
Chan said that during their operation, the police confiscated HK$130,000 in cash and found receipts for supermarket coupons worth HK$165,000.
"We seized receipts mentioning that 3,300 coupons had been purchased. We also seized some arrows, some weapons. We do not exclude the possibility that the fund was used as a reward to encourage teenagers to come out and join in the civil unrest," he said.
Last month, local media reported that HSBC was to close a corporate account the group was using to collect the donations, because its activities did not match the business purposes stated by the client.