An 80-year-old man is one of three people charged over a large cannabis crop in south-western NSW that police estimate had a street value of $5.5 million.

The elderly man and two other men - aged 47 and 54 - were arrested on a farm in Colinroobie, about 70 kilometres east of Griffith, on Thursday morning after police allegedly discovered more than 2500 cannabis plants growing there.

Police arrested three men over the cannabis crop at Colinroobie. Credit:NSW Police

Officers also allegedly discovered two shotguns, two rifles, ammunitions and cash when they searched the property, on Males Road.

The men were arrested and taken to Griffith Police Station, where they were charged with cultivating a large commercial quantity of prohibited plants.

The trio were refused police bail, and are due to appear in Griffith Local Court on Friday.

The drug raid was carried out by Strike Force Elkmont, comprising officers from the Griffith Local Area Command, in conjunction with Strike force Hyperion, comprising officers from the State Crime Command's Drug Squad.