Scammers are preying on the families of Chinese students in Australia amid a rise in virtual kidnappings.

Four instances have been reported in the past month, with victims receiving threats unless they pay between $175,000 and $250,000.

The total amount demanded exceeds $750,000.

A "virtual kidnapping" is an extortion scam that involves young people being told they have been implicated in a crime and need to pay money to avoid deportation or being placed under arrest, police said on Friday. 

Initial contact is often made through a phone call from someone usually speaking in Mandarin and claiming to be a representative from a Chinese authority, such as the Chinese embassy, consulate or police.

Using technology to mask their physical locations, scammers encourage victims to continue communications through encrypted applications such as WeChat and WhatsApp.

The victim is then threatened or coerced into transferring large amounts of money into unknown offshore bank accounts.

As the scam escalates, the victims are coerced into faking their own kidnappings before the scammer sends these images to their family and demands ransom payments for their safe 'release'.

NSW Police's Serious Crime Squad commander said detectives are working closely with universities and the Chinese embassy and Chinese consulate in Canberra and Sydney.

"It is disgraceful there are scammers out there preying on international students who have come to Australia to study; most of whom are living in a new country and far away from loved ones for the first time in their lives," Detective Superintendent Joe Doueihi said.

The detective urged victims to come forward but acknowledged many may feel traumatised or embarrassed.

"There is no shame in coming forward to NSW Police for assistance," he said.

In one recent case, a 22-year-old woman said she received a phone call from a person claiming to be a Chinese police officer alleging she was implicated in a crime.

She would have to pay to prove her innocence, she was told.

The young woman transferred $20,000 into an offshore account before the scammer demanded she fake her own kidnapping in a hotel to secure an additional $174,000 from her family in China.

Investigators managed to locate the woman safely before any further money was paid.

Another woman, aged 18, was told by a supposed Chinese police officer she would be deported unless she paid $280,000.

After being told to stage her own kidnapping to send images to family so the fake debt could be paid, she was found safe in a hotel in Sydney's inner west.

One family parted with $270,000 to secure the supposed release of their 23-year-old daughter after she was told she had delivered a package overseas that had been seized by Chinese police.

The woman was located safe in a Sydney hotel in early May, police said.

China's consulate-general in Sydney and an official from the embassy in Canberra joined NSW Police in the awareness campaign on Friday.