A cyclist, stopped for not wearing a helmet, was discovered to be hiding a sawn-off shotgun down his trousers, police say.

The 35-year-old man was riding through Fairview Downs in Hamilton in the early hours of this morning, when two police constables on patrol pulled him over for looking out of place and not wearing a helmet.

"When they were talking to him [they] noticed a shotgun cartridge fall to the ground as he emptied his pockets," Hamilton city area commander Inspector Greg Nicholls said.

"A subsequent search revealed the 35-year-old man had a sawn-off double barrelled shotgun concealed down the front of his trousers and another round in his pockets.


"The man told officers he had the firearm for protection and had gone out earlier in the evening to test that it worked."

He was arrested for unlawfully carrying a firearm, unlawful possession of a firearm and ammunition. He will appear in Hamilton District Court later today.

Mr Nicholls praised the work of the two officers, saying they had followed their instincts to uncover a crime.

"What started as a routine stop ended up by removing the risk to the public posed by a firearm being illegally in possession of a person well known to police," he said.

"Anyone who believes they have sufficient grounds to fear for their safety is urged to contact the police and not place themselves, and others, at further risk."