Officers executed a search warrant at the semi-rural property at Schofields on Sydney's northwest fringe about 7am on Tuesday morning.

They found 2080 cannabis plants with an estimated street value of $5.8 million and arrested two men and a woman at the property.

An hour earlier, a 28-year-old man had been arrested at a unit in the Sydney suburb of Rhodes, where police also seized mobile phones and cannabis.

Police say the 28-year-old is the ringleader of a large organised crime syndicate involving the cultivation and supply of cannabis across the state.

All four have now been charged.

The arrests are part of Strike Force Hyperion, an almost year-long investigation into outdoor cannabis cultivation across Sydney.

Strike force detectives seized 2379 cannabis plants from a Campbelltown property last month, making five arrests.

Police say that property was linked to the same syndicate.

"Just across two properties, this criminal syndicate has earned in excess of $12 million from cultivation of cannabis," Detective Acting Superintendent Jayne Doherty told reporters on Tuesday.

"We're confident there have been a number of cultivations from each of the properties."

Both properties just looked like regular rural properties growing plants, Ms Doherty said.

But the electricity at the Schofields property had been bypassed and the house was used to propagate juvenile cannabis plants.

"These groups are funding other criminal activity within our country and that's why we will take every step address them and to cut them off," she said.

The 28-year-old was refused bail to appear at Burwood Local Court on Tuesday. The three others were refused bail to appear at Blacktown Local Court on Wednesday.

Australian Associated Press