Police say criminals have targeted Chinese, Vietnamese and Indian communities, describing on Thursday a string of incidents where fraudsters purporting to be officials fleeced victims in Sydney.
The scammers claim to be from embassies or foreign police forces and accuse victims of fictitious overseas crimes.
Victims are threatened with deportation or extradition unless they pay up.
The targets reported receiving multiple aggressive calls over several days and being transferred between scammers to lend the fraud authenticity.
The Vietnamese consulate in Sydney told AAP the behaviour, dubbed authority scamming, is often the work of overseas syndicates that are hard to track down.
The consulate had started receiving reports of suspicious calls six months ago, some declaring they had lost tens of thousands of dollars, it said.
In one incident highlighted by NSW Police, fraudsters masquerading as Vietnamese embassy officials accused a western Sydney woman of money laundering and then claimed a man carrying her passport had been arrested in neighbouring China.
She was warned she would be arrested and escorted to Vietnam within a week.
Armed with the woman's personal information, the extortionists demanded she prove her innocence by paying money into a foreign bank account.
Under daily harassment, the woman reported losing $57,000.
It comes after Victorian police estimated almost 200 people in Australia, predominantly Chinese students, were tricked out of more than $7 million.
Culturally and linguistically diverse communities are more vulnerable to scams, with the government's ScamWatch service reporting they lose on average twice as much per person as other victims.
Australia's extradition treaties with India and Vietnam mean people wanted for crimes in those countries may plausibly fear being forced to return, making it harder for victims to dismiss the callers' threats.
Police say scammers often spoof foreign phone numbers so they appear Australian, luring victims onto encrypted phone apps like WhatsApp and Viber.
"Scammers are highly adaptive and will target people they believe are more vulnerable at any given time," NSW Police told AAP.
"That can include where language barriers, unfamiliar systems or fear of authority can be exploited.
"Offenders constantly change their tactics and target groups, which is why ongoing community awareness and early reporting are so important."
Both the Vietnamese and Indian embassy websites broadcast warnings urging would-be victims to terminate and report menacing calls, and reiterate officials will never request money or make threats to secure legal compliance.
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