Police have made what they say is Australia’s biggest ever cocaine seizure, uncovering 2.7 tonnes of the drug buried in secret bunkers at a property on Sydney’s western fringes.

The seizure was made by the Australian federal police on Friday at a semi-rural property in Londonderry.

Two men aged 21 and 25 have been arrested and charged with possessing a commercial quantity of an unlawfully imported border-controlled drug.

Police allege they found the drugs in plastic tubs buried in underground bunkers concealed beneath three shipping containers on the property.

They said the cocaine had an estimated street value of about $816m, equating to about 3 million “street-level deals”.

Police allege the cocaine was imported into Australia near Midge Point in north Queensland and brought to Sydney “at the behest of a Sydney organised crime group”.

The seizure was part of Operation Minjiang, a joint investigation by the AFP alongside Queensland police, the Australian Border Force and other agencies. It began after 40kg of cocaine was allegedly found in the water off a boat ramp at Midge Point on the Whitsunday Coast.

An alleged “mother vessel” suspected to be part of a drug importation enterprise, MV Wealth, has been detained in the Solomon Islands.

The two men arrested on Friday appeared before a NSW local court on Saturday and were remanded in custody. They are next expected to appear before Penrith local court on 13 August.