A Greek Orthodox nunnery was turned into a marijuana plantation by two men posing as gardeners for elderly nuns, police said.

Acting on a tip-off, officers raided the nunnery in the village of Filiro, near the northern port city of Thessaloniki, and found more than 30 large cannabis plants in the enclosed garden.

"Two unknown men had told the two elderly nuns in the nunnery they would like to help them with the garden and then proceeded to plant the cannabis," a police official told Reuters.

"The nuns did not know what they were and assumed they were large decorative plants," he said.

Police did not arrest the nuns and have launched a hunt for the culprits.