Two men have been charged with cultivating about 9,000 cannabis plants on two leased rural properties within the Chaelundi National Park near Dorrigo.
Two men were seen watering the plants about midday (AEDT) on Wednesday, police said.
"A search warrant was conducted on the property with the two men, aged 61 and 37, arrested and taken to Coffs Harbour police station," police said in a statement.
"Police allegedly located in excess of 9,000 cannabis plants with an estimated potential street value of $18 million." Two men have been charged with cultivating cannabis greater than a commercial quantity and after a brief court appearance were refused bail to next face Coffs Harbour Local Court on March 9.
Police say they raided two properties as a result of the men's arrests and seized cash and financial documents.
