A man drew some unwanted attention in Auckland last night by allegedly using nitrous oxide while driving past police.

Police said he was subsequently found with a loaded shotgun and cannabis after his vehicle was searched.

The incident unfolded on Greenwood Rd in Māngere just after 10.30pm when a vehicle attracted the attention of officers.

“Police had sighted the driver using nitrous oxide before stopping the vehicle,” Senior Sergeant Steve Albrey said.

He said there was a "strong odour" of cannabis coming from the car, and police searched the vehicle.

“They located over 160 grams of cannabis plant in the boot, as well as a loaded and cut down semi-automatic shotgun and ammunition,” Albrey said.

The man was arrested following the search.

A 21-year-old man was due to appear in the Manukau District Court today, charged with possessing an offensive weapon, unlawfully possessing ammunition, possessing cannabis for supply, and breaching the Medicines Act.

“We’re very happy to have a dangerous weapon off the street and a considerable amount of cannabis that was set for sale,” Aubrey said.