As terrifying as it may seem, hostages who are half-naked, bound and bleeding are having ransom videos of them being sent to their families overseas. 

However, they are all staged - and it's not by choice. 

"They are convinced to fake their own abduction and kidnapping and then send images of themselves in vulnerable positions to family," Detective Superintendent Joe Doueihi said. 

It's an elaborate scam that is targeting Chinese students.  

Relentless calls convince them they are speaking with government officials accusing them of a crime.  

Threatened with arrest and deportation - they are then pressured into faking their own kidnapping so their families pay a ransom.   

"These scammers are very, very convincing," Doueihi said. "It's embedded in Chinese culture to respect authority." 

On Sunday the family of a 23-year-old woman in Sydney transferred almost $300,000.  

Two days earlier, one was demanding half a million dollars, and earlier in the month a man was held hostage. 

He had gone to meet people who were posing as police and was handcuffed for a couple of hours at one location. 

"I would say more than likely they were also victims of this scam - pretending to be Chinese police officers on behalf of the scammers." 

But it's not just happening in Australia.  

Scammers were paid $600,000 by two students in Auckland after cold calls convinced them their families were involved in offshore crimes.  

Australian police are worried the criminal network is becoming more sophisticated.  

"Some of our victims are travelling to Cambodia and Thailand and others to other states in Australia." 

Police are urging everyone to be on alert and contact the Chinese consulate to verify any allegations.