The police commissioner on Friday warned the public to be on guard, amid a rise in investment scams in recent months, with most cases involving cryptocurrency.

Raymond Siu revealed that the frauds usually begin with fake romances - scammers would show concern for their target before providing them with a link.

He emphasised the cases were too good to be true, and the public should never fall for them.

The police chief also said there had been a surge in cases in which scammers pretended to be mainland officials.

"Whenever the caller claims to be an official from the mainland, and says he - or she - is investigating a case etc, you can actually hang up immediately," he said.

"Even if they don't ask for money, you can hang up right away. These must be scams."

He added that the force is working to roll out more measures to combat scams targetting students from the mainland, and hopes to intercept the cases at sources.