Officers on Sunday also urged schools to be on their guard against phone fraudsters after syndicate members were found in some cases to have pretended to be headmasters or teachers to trick janitors into transferring money to them.

Police said these victims only realised they had been cheated when they later called the genuine headmasters and teachers.

The suspects, aged 23 to 44, were arrested on Friday and Saturday in a series of raids and included three domestic helpers.

The three men and three women were arrested on suspicion of conspiracy to defraud and money laundering, said Senior Inspector Luk Hung-kei of the commercial crime bureau’s fraud unit.

“The syndicate is believed to have operated since last November,” Luk said. “After thorough investigation, we took action and arrested six people in raids on various premises across the city.”