Canberra police said one family even mortgaged their home in China earlier this year in order to pay scammers threatening their daughter in the capital.

It's an increasingly complex deception that's ensnared vulnerable people from non-English speaking backgrounds across the country, run out of "boiler room" call centres overseas or on shore. But while the danger is not the physical horror families believe, its toll can still be devastating.

The Australian Federal Police has issued a second warning to universities and the public at the start of semester two after uncovering a nest of scams hitting students at the Australian National University.

Detective Senior Constable Mathew Tonge of the AFP's International Operations team said there had also been cases in other jurisdictions, but did not say how many students were affected.

"We've sought to reach out initially here in Canberra because we are aware there is an active environment in which ANU students are falling victim," he said.

Within a syndicate's "pressure cooker" churn of calls, police say victims are often bounced around between multiple people claiming to be from the Chinese embassy or "Chinese Public Security Bureau".

They might be told their personal information has been compromised, their visa is in trouble or they are implicated in a crime. A package has arrived for them full of fake credit cards. Or they are wanted for tax avoidance and will be arrested unless they pay up.

The number on the screen will usually look legitimate, the caller will refer them higher "up the chain" or even offer seemingly benevolent advice about their safety or diet, all the while plying them for more information with which to build the scheme.

Eventually, in some of the most elaborate and frightening scams, victims are talked into leaving home and checking into a hotel, severing all contact with family and friends, even taking staged abduction photos of themselves, unaware that the people on the other end of the line have now begun making ransom demands on their family back home.

When relatives can't make contact, they often pay up.

"Students may be from wealthy families back in China or [scammers] might send out a text or cold call at random," Detective Senior Constable Tonge said.

"They build trust, they make the victim rely on them more and more. They might be told the online compromise has extended to their location so they need to get away for a while, they shouldn't use their phone. They make you think they are there to protect you.

"The victim becomes effectively a virtual hostage even though they don't realise it themselves. This is organised crime."

This kidnap fraud first emerged in Canada about 18 months ago and has now reached Australia, including the ACT, police said. It's one of a number of socially-engineered extortion rackets to evolve in the modern age, including the high-profile ATO scam.

In May, police worked with Border Force to turn back a group of 15 Taiwanese nationals suspected to have flown into Brisbane to set up a scam boiler room. Other operations have been uncovered holed up in houses and hotels.

International students who spoke on condition of anonymity said they already feared the Chinese government was watching them in Australia.

"If you get a call from Chinese government, you do what they say," one student said.

Another said he worried about his visa and his family back home. While he had not been contacted by a scammer himself, he was not surprised when he heard of other students at his university being duped earlier this year.

"We don't want to mess up our visa," he said. "It makes sense students would go along."

Detective Senior Constable Tonge said scammers exploited people's faith in authority figures, while leveraging their own understanding of Chinese culture and language.

"If you're studying here far from home, on your own, you're already trying to get used to a foreign country," he said.

"The impact of this can be really terrible."

Scammers were increasingly directing victims to communicate via encrypted apps like WhatsApp and Wechat which are harder for police to trace.

"This is a generation reliant on the internet and social media now to communicate, so it's familiar to them," Detective Senior Constable Tonge said.

"This is an old crime with new technology...but syndicates are harnessing it to get better at this."

Many cases were not reported at all, as students tried to save face with their families back home. Others were instructed to perform a hard factory reset on their device, destroying evidence.

ACT Policing said that, while they had made no arrests in relation to these scams, they were aware of cases where victims paid tens of thousands of dollars at a time.

While multiple students and staff at ANU said they were also worried about scammers following revelations in June of a huge data breach at the university, both the AFP and ACT Policing said they were not aware of any scams connected to the hack.

Last year, the full range of scams reported to the Australian Competition and Consumer Commission cost Canberrans more than $3 million, and half a billion nationally.

Acting manager of international engagement at the AFP Steven Evans said police were starting to crack down on scam syndicates, sharing information with international law enforcement, as well as the Chinese embassy.

He stressed Chinese officials would never contact citizens in Australia directly about legal matters, instead reaching out through local authorities.

Police urged people who had been contacted in this way to talk things over with friends and family or local authorities before following advice and to look out for friends suddenly withdrawing or behaving oddly.

"If it in doubt or you've already been exposed, report it. You won't get in trouble."

If you have feel you may have been targeted or have information, contact police on 131 444 or on Crime Stoppers on 1800 333 000.

For more information on scams, how to report them and tips on how to protect yourself, visit the government's Scamwatch website, the ACSC's CyberOAK page, the ATO's verify or report a scam page, or contact your local police station.

If you are concerned that your identity has been compromised, contact IDCARE.

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