Prison officers discovered a swag of contraband stashed inside garbage bags in a shed outside Glen Innes Correctional Centre on Sunday afternoon following a secret month-long investigation.

Syringes and needles, tablets, tobacco, cigarette lighters, vials of testosterone, and a mobile phone charger were among the items seized.

A jail-made tattoo gun, nearly 100 tattoo needles, containers of tattoo ink and a tattoo power station were also found.

Corrective Services NSW Commissioner Peter Severin said the discovery, which followed several tip-offs and extensive surveillance, should serve as a warning to all inmates.

"Our staff are well trained and have the necessary tools to detect and prevent contraband from circulating through our centres," he said in a statement on Monday.

Anyone caught smuggling contraband into jail faces two years' in prison.

Australian Associated Press