Joe Chan Chi-yung, chief inspector in the force's technology crime division, said it was common for fraudsters to advertise low-skilled summer jobs online.

During the hiring interview, job seekers were asked for their identity cards for photocopying. However, the fraudsters ran away with the identity cards and later used them to borrow money from loan sharks or to buy iPhones, Chan said.

In some cases, the victims were forced to repay the loan.

Those whose identity cards were used to buy iPhones would have to pay the monthly instalments for the phones after the fraudsters had picked them up.

In a couple of cases police dealt with last year, job applicants were told to use fake address proofs to apply for loans from financial companies in exchange for a reward of 35 to 50 per cent of the loan amount. A total of HK$910,000 was involved.

'[In those cases,] the job applicants now become criminals, because they agreed to take part by using fake address proof to borrow money,' said Maxim Kwok Mei-sum, chief inspector in the commercial crime bureau's fraud division.

Police said they had made some arrests last year but refused to go into details as the investigation was still under way.

They said the identity card scam stemmed from what they referred to as a 'secret customers trick' that was used last year. In those cases, fraudsters posed as providers of a 'mystery customer' service and hired victims as service sleuths to test the service quality of financial companies. In fact, the victims were taking money for the criminals.

Kwok also warned job applicants of the popular model agency scams, in which victims were conned into paying a hefty tuition fee for model training before they could be qualified for modelling jobs that didn't exist.

Pyramid selling schemes are another trap for summer job hunters, Siu Wai-sing, chief inspector in the fraud division, said.