A record 1.2 tonnes of methamphetamine has been seized in Western Australia and eight men have been charged over the $1.04 billion drug bust.

The six-month, multi-agency investigation is the biggest drug haul in Australian history, trumping the 903 kilograms seizure in Melbourne earlier this year.

Police allege a vessel called Valkoista arrived in Geraldton, in WA's Mid West region, about 2am on Thursday and the drugs were then offloaded into a white van just before 4am.

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About 1.2 tonnes of methamphetamine has been seized in Western Australia in the biggest haul in Australian history

The seizure tops a 903kg seizure in Melbourne earlier this year (pictured are some of the men arrested)

Police described the bust (pictured) as being the result of a 'complex, multi-agency investigation which traversed the country'.

Officers intercepted the van as it reversed from the dock, allegedly finding 59 bags containing about 20kg of methamphetamine.

Police arrested the three people inside, including a 33-year-old man from southern Sydney and two other men from NSW, aged 38 and 52.

Officers also boarded Valkoista and arrested three crewmen including a 45-year-old man from the NSW Central Coast and two men from South Australia, aged 48 and 44.

A bag containing about 20kg of methamphetamine was found on the vessel.

Eight men have been charged over the $1.04 billion drug bust involving a boat (pictured) in Geraldton on Thursday

Police arrested the three people inside, including a 33-year-old man from southern Sydney and two other men from NSW, aged 38 and 52

Officers intercepted the van as it reversed from the dock, allegedly finding 59 bags containing about 20kg of methamphetamine

The Australian Federal Police display bags containing over $1 billion worth of meth seized

Eight men were arrested and charged in connection with the bust, shown here on display

Police believe the drugs originated from China and were destined for the east coast.

A further 20 search warrants were conducted at residential properties in Sydney, the NSW Central Coast and Adelaide.

Two men from South Australia, both aged 37, were later arrested at a Perth hotel.

Charges include importing a commercial quantity of a border controlled drug, and possessing a commercial quantity of a border controlled drug reasonably suspected of having been unlawfully imported.

Police believe the drugs originated from China and were destined for Australia's east coast

Officers also boarded Valkoista and arrested three crewmen including a 45-year-old man from the NSW Central Coast and two men from South Australia, aged 48 and 44

A further 20 search warrants were conducted at residential properties in Sydney, the NSW Central Coast and Adelaide

Both offences carry a maximum penalty of life behind bars.

'We're confident this will make a big dent,' an Australia Federal Police spokesman told reporters on Friday.

Police described the bust as being the result of a 'complex, multi-agency investigation which traversed the country'.