Security Secretary Chris Tang on Sunday warned of a significant rise in a new type of traffic-related fraud, with the police having received more than 70 cases.

He explained the new play-book of fraudsters during a radio programme.

"In traditional 'crash for cash' fraud, criminals would pretend there had been a car crash. They pretend that they were in the crash or that they were hit, and then they blame you and try to extort money from you, " he said.

"Recently, fraudsters would drive around with dashcams and when they catch a driver crossing double white lines, they use the footage to file a police report.

"They then keep an eye on the case patiently and wait until the driver pays the traffic fine before contacting the driver and claiming that they were the car behind and had to brake suddenly because of the cut-in.

"They also claimed that they suffered a neck injury and psychological distress, and demanded tens of thousands in compensation."

He said that in one case, someone who claimed they were a victim said they had suffered 20 separate injuries to their neck.

Tang said it is very unlikely that one person could be that unlucky to suffer such a series of injuries so officers think that the scam is organised.

He noted that the same few law firms and doctors keep appearing in these compensation cases.

While officers won't jump to conclude there is collusion, they will investigate thoroughly and take action if they find any illegal activity, Tang added.