Dozens of officers combed the greenhouse and seized almost 11,000 of what they claim are cannabis plants after raiding the property on Killarney Gap Road at Rocky Creek in the early hours of Thursday.

Oxley police led the strike force, backed by the Western Region Enforcement Squad, the Public Order Riot Squad, detectives and other officers surrounded the property about 3am.

One woman and five men were arrested at the scene and taken into custody at Narrabri Police Station for questioning.

They were all later charged with knowingly taking part in cultivating a large commercial quantity of cannabis.

The six were refused bail and spent the night in custody on Thursday.

The 41-year-old woman will front Tamworth Local Court today, while five men - aged 28, 33, 35, 45 and 56 - have been ordered to appear in a New England court.

The raid - and huge multi-million-dollar seizure - is the culmination of a three-month investigation by a secret squad of police.

Code-named Strike Force Lyretrail, detectives launched the operation in September after a tip-off about the cultivation of cannabis at a remote farm near Narrabri.

After months of secret investigations, officers moved on Thursday and uncovered 10,928 of what they claim is cannabis plants - some as two metres tall. Cannabis seeds were also discovered and seized, police said.

The Leader understands some of the plants are worth as much as $2000 each in street value.

Police will allege in court the plants have an estimated street value of $21.8 million.

Officers spent the day combing the property and said investigations are continuing into the haul.