Police have rounded up 682 people in a citywide operation targeting scams, technology crimes and money laundering, with officers dismantling several syndicates including a family-run online romance scam ring.

The force on Monday said the individuals were arrested on suspicion of conspiracy to defraud, obtaining property by deception and money laundering during the three-week operation.

The suspects were allegedly involved in 580 cases with losses amounting to HK$620 million in total, according to police.

During the period, officers arrested 11 people in relation to an online romance scam syndicate and a money laundering ring, which allegedly conned 314 people out of HK$44 million.

Chief inspector Lee Chun-man, of the Cybersecurity and Technology Crime Bureau, said some suspects allegedly posed as young women living abroad on dating apps to talk to the victims.

"When the relationship between the two parties reached a certain level, the syndicate allegedly posed as the young woman's superior or overseas police officers, claiming that the woman had unfortunately passed away," Lee said.

"The suspects also forged business cards and proof of estate, and said the woman had designated the victim to manage or inherit the assets, to ask the victim to pay fees."

Lee also alleged that members of the syndicate had impersonated police officers and reached out to the victims again, pretending that the case had been solved and demanding them to pay administrative fees to get back the money they had lost.

Officers also said the ring allegedly processed crime proceeds with the help of a separate money laundering syndicate using stooge bank accounts.

The syndicate was said to convert the proceeds into cryptocurrencies before cashing out, Lee added.