Cops make biggest-ever ice precursor bust

Tonnes of the deadly drug ice have been prevented from reaching Australia's streets after authorities pulled off the largest seizure of precursor chemicals in the nation's history.

Two consignments from Thailand - 3.9 tonnes of liquid ephedrine concealed in green tea bottles and 350 kilograms of methamphetamines hidden inside buckets of plaster - were intercepted in the past three weeks.

The ephedrine would have produced 3.6 tonnes of the drug with a street value of $3.6 billion.

Three people have been arrested for trying to import the drugs into Sydney.

So far this year authorities have intercepted more than seven tonnes of illicit narcotics in total headed for Australia.