Australian federal police have seized 384 kilograms of cocaine – which they value at around R1.4 billion – in the biggest ever drug interception operation by its border police.

The drugs were welded into the arm of a giant, yellow, Cat excavator, shipped in from South Africa.

Police say the concealment attempt was "incredibly sophisticated".

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Australian border police have arrested two men in New South Wales and seized 384 kilograms of cocaine in the biggest ever single drug bust in the history of its federal police force.

The stash represents almost half as much as the total of all cocaine detected at Australian borders last year.

Police put the street value of the find at the equivalent of R1.4 billion.

The drugs were found welded into a giant, yellow Cat excavator shipped from South Africa. The exact local origin is not yet clear.

The arrests came after what police described as a "controlled delivery" of the earthmoving machine, after the drugs were found via X-ray imaging despite "incredibly sophisticated concealment" that gave no external hint the machine had been tampered with.

Police said it took them two days to open the second-hand excavator, remove the cocaine, substitute it with a dummy payload, and return it to its original condition before allowing it to continue on to its destination.

Residents in the town of Bugendore described a dramatic raid during which heavily-armed police – apparently after months of surveillance – crashed a vehicle through a gate as part of a tightly coordinated operation.

Though its origin is not yet known, the cocaine is believed to have been headed for Canberra and more rural parts of Australia, including its Snowy Mountains region, now in its skiing season.

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