In addition people lost more, with the financial toll rising from HK$3.2 million in 2010 to HK$6 million.

Police defended the low arrest rate by saying that many of the fraudsters came from the mainland and once their scams were sprung, they quickly headed back over the border, making arrest difficult.

'If the swindlers are from the mainland, they can escape very quickly after committing crimes,' said Chief Inspector Fanny Kung Hing-fun of the commercial crime bureau. 'This makes it much more difficult for us to make arrests and crack down on deception cases.'

Most criminals work in gangs while undertaking their deceptions.

'The males act as lookouts, while the females play the tricks,' said Detective Senior Inspector Simon Kan Chi-siu. 'They're well-organised. Sometimes we have even found them to have pre-written scripts.'

Most street scams involve familiar tricks, such as offering victims spiritual blessings to con money out of them. During this scam, as well as paying cash the victim is often asked to hand over an object of value, such as jewellery they are wearing, to be 'blessed' to bring them luck or money. The object is wrapped up by the con woman while she passes her hands over it to 'bless' it. The victim is given back the wrapped object and told not to open it for seven days. When they do unwrap the object it is not what they handed over and their property and cash are both gone.

Lawmaker James To Kun-sun, who is chairman of the Legislative Council's security panel, urged the police to exert greater efforts and make street scams a top priority.

'No one robs with guns anymore; it costs a lot to buy a gun,' he said. 'But street scams are different; it can be easy to swindle hundreds of thousands of dollars from the elderly.'

The latest arrest was made last Friday when five people from Guangdong were held for attempting to obtain HK$300,000 from an elderly woman in a spiritual blessing scam in Tuen Mun. The 72-year-old was approached by three of the suspects in a park. They claimed they knew her son was having a run of bad luck and suggested a ritual to help. Police arrested them, plus two lookouts, when the woman was about to go to a bank to withdraw money.

The public - in particular the elderly - were again reminded by the police to ignore such storytellers, especially during the first month of the Lunar New Year when such criminals were more active, Kung said.

Out of all four major categories of street deception, only sales of fake electronic parts recorded a drop in the past two years.