Canterbury Metro Area Commander Superintendent Lane Todd said the officers spotted a stolen car at a fast food restaurant on Ferry Rd at 7.50pm.
"A 3D-printed firearm was located during a subsequent search of the car and has been seized.
"A 20-year-old gang member and a 17-year-old gang associate have each been charged with two counts of unlawful possession of a firearm/restricted weapon, and one of unlawful possession of ammunition.
Todd said the 20-year-old was set to appear in the Christchurch District Court on Friday and the 17-year-old in the Christchurch Youth Court.
ENDS