More than $5.3 million of property, cars, cash and other assets have been frozen in Whanganui and the central region under a contentious law used to target gangs.

The Criminal Proceeds (Recovery) Act 2009 allows police to freeze and take someone's assets without ever finding them guilty of any criminal activity or even laying criminal charges.

The Government said the law gave police greater abilities to stifle gang activity, but lawyers said the move was an over-reach and brought fundamental civil liberties into question.

Assets worth $5.3 million have been restrained in the central region under civil forfeiture laws since 2009. Sixty-four assets have been restrained, and 30 have been sold, totalling $841,000.

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Just under $600,000 of the proceeds was made available to fund law enforcement and health initiatives.

It wasn't clear how many assets were still restrained or if any had been returned to the owners following the legal process.

Police Minister Judith Collins said the act had been working effectively.

"Police have been extremely successful in investigating and seizing the dirty money of criminals and gangs since the Government passed this legislation."

She said 88 per cent of restraints and 96 per cent of forfeitures have been linked to drugs and/or organised crime.

"Gangs, organised crime, drugs and family violence drive much of police daily workload, and reducing these harms and crimes is a priority for the Police Commissioner and the Government."

She said the outcome of cases was determined in court.

Assets that police suspected had been acquired as a result of criminal activity can be restrained and forfeited to the Crown on the civil standard of proof, "the balance of probabilities", which is a lower level than the criminal standard of "beyond reasonable doubt".

The removal of a criminal conviction necessary for asset forfeiture was a significant change from the old legislation, the Proceeds of Crime Act 1991, said lawyer Graeme Edgeler.

Mr Edgeler said it was not fair for the Crown to take someone's house, cars and savings without proving any criminal activity.

"The Government should not have the power to punish you unless it can prove to a pretty high standard that you've actually done something illegal," Mr Edgeler said.

"Even if there's a 49 per cent chance you're completely innocent, that the Government can take everything you've worked for away is pretty serious."

Labour police spokesman and MP Stuart Nash said he supported the law, but only if the offending was proven in court to a criminal standard.

"If you gain wealth or assets out the proceeds of crime, you should hand them back to the state when you get caught.

"I would be very uncomfortable with seizing citizens' assets without proof of guilt. Reasonable probability is not strong enough."

He said he was concerned about the act seemingly being used to target gang activity but not other forms of organised crime.

"I suspect [it is] because targeting gangs make good headlines, and every Government likes to be seen to be tough on gangs, whereas white collar crime [is] not as newsworthy," he said.

Nationwide, $435 million of assets have been restrained, and $66 milllion worth has been sold. More than $326 million worth of assets remained frozen while legal proceedings take place. The $36.8 million paid into the Proceeds of Crime funds can be bid on by law enforcement and health agencies to fund projects, including alcohol and drug treatment programmes, customs drug screening and legal costs.