US national Justin Wetherbee pleads guilty after being charged over record cocaine haul linked to Mexican cartel

Police stopped 2.4 tonnes of cocaine from getting into Western Australia — said to be the biggest drug bust in Australia's history.  (Supplied: WA Police)

A second person in as many days has admitted their involvement in Australia's biggest ever drug bust that saw $1 billion worth of cocaine — linked to a Mexican drug cartel — seized by police in Western Australia.

American Justin Lujan Wetherbee, 39, was arrested at the end of December last year, amid a secret police investigation that started after the US Drug Enforcement Administration intercepted the 2.4 tonnes of cocaine off the South American coast.

WA police then used plaster of Paris to make fake cocaine, which they packaged up, dropping half of it in nets in the Indian Ocean off the coast of Perth.

As police watched on, the crews of two boats — Cool Runnings and Catalina — sought to retrieve the packages.

Cool Runnings washed up on a beach near Moore River, 70 kilometres north of Perth, and three men were arrested.

Footage of what's believed to be Australia's biggest drug bust.

The crew of Catalina then tried to retrieve the Cool Runnings cargo, but after taking the fake drugs off the vessel in a mid-ocean transfer, Catalina sank.

A further nine people were charged in the days and weeks that followed, including Wetherbee who was arrested at his hotel in the Perth metropolitan area.

Another was Kenny Chee, 27, from New South Wales who was found at an address in suburban Carlisle in early January.

Guilty plea over cocaine seizure

On Tuesday, in the Perth Magistrates Court, Chee pleaded guilty to trying to take possession of 200 kilograms of the cocaine and was remanded in custody until he's sentenced in the District Court.

Wetherbee made his third court appearance on Wednesday in the Joondalup Magistrates Court.

Cash was seized from a vehicle in Coolgardie as part of a the record cocaine bust. (Supplied: WA Police )

He appeared via video link from Hakea prison and pleaded guilty to a charge of attempting to possess cocaine with intent to sell or supply to another.

He was again remanded in custody until he faces a sentencing hearing later this year.

Both he and Chee face maximum jail terms of up to 25 years.

Cool Runnings washed up at Guilderton, north of Perth, and three crew members were arrested. (Supplied: WA Police )

However, it is expected they will be given a hefty discount for their early pleas of guilty, which is regarded as co-operating with authorities and sparing taxpayers the cost of a trial.

The other 10 people who were charged have their next scheduled appearances in court next month.