Police have charged four people allegedly involved in an "elaborate" multi-million dollar money laundering scheme that smuggled cash and washed millions of dollars through Australian businesses.

The Australian Federal Police (AFP) has seized properties and luxury cars across New South Wales and Queensland allegedly purchased with "tainted money" and have frozen bank accounts — all worth more than $21 million.

AFP Detective Superintendent Adrian Telfer said it's alleged the group washed millions of dollars in the proceeds of crime through "multiple Australian businesses".

He said some of the businesses involved had both legitimate and illegitimate arms, which made the investigation complex.

"This investigation has unravelled a sophisticated operation that allegedly moved illicit cash around the country using [cash] dead-drops and couriers, before washing it through a network of seemingly legitimate businesses in south-east Queensland," he said.

Detective Superintendent Telfer said dead drops — where cash was left at a pick-up point like a park or in a car — were a hallmark of organised crime and something police had long been dealing with.

Police say the cash was sent to Queensland as cargo on domestic flights before being picked up by couriers from a security company.

It's alleged those charged relied on their "ill-gotten profits" to develop property portfolios and purchase luxury cars and cryptocurrency.

At the heart of the 18-month joint investigation was a Gold Coast-based security firm which offered armoured transport services to clients.

Police say that business transferred cash and other valuables between businesses and banks, and converted $190 million into cryptocurrency.

The investigations into the source of that money are ongoing.

It's alleged that business was mixing cash from its legitimate business arm with illicit funds deposited from suspected criminals.

Some of those businesses allegedly involved were a sales promotion company, a classic car dealership and cryptocurrency exchange services.

On June 5, police charged a 32-year-old man, who is alleged to have been linked to the "majority" of the restrained properties and a "client" of the security firm.

He's alleged to have controlled a sales promotion company that received about $9.5 million in cash and cryptocurrency originating from the security company over 15 months.

The 32-year-old has been charged with money laundering as well as failing to give up the password to his mobile phone.

A 48-year-old man and the 35-year-old woman, who police allege owned the security firm, were charged on June 6.

A 58-year-old Brisbane man who they allege was the director of the classic car dealership which received around $6.4 million from the security firm has been charged and is due to face Brisbane Magistrates Court in August.

A Queensland Joint Organised Crime Taskforce (QJOCTF), comprised of the AFP, Queensland Police Service, Australian Border Force, the Australian Criminal Intelligence Commission, AUSTRAC and the Australian Taxation Office worked on the investigation.

Detective Superintendent Telfer said police started to investigate "suspicious financial transactions" in December 2023 and is ongoing with the potential for further arrests.

"Money laundering is the lifeblood of organised crime," Detective Superintendent Telfer said.

Source: Australian Broadcasting Corporation.