A Northland man who died after a cannon-type weapon accidentally discharged had more than 20 years' experience as a firearms instructor.

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Derek Allan Kelly, from Mahuta, was killed yesterday when he removed the weapon from the back of his ute and it went off.

The 74-year-old had been a member of the New Zealand Mountain Safety Council's firearms instruction team for more than two decades.

Its Firearms and Hunter Safety programme manager Nicole McKee said Mr Kelly taught thousands of people about how to handle firearms safely.

"This is a great tragedy not only for his community in Mahuta but for Northland itself.

"He was a wonderful man that's given a lot of volunteer time to helping out his community and teaching safety to everybody up there.

"And it's an absolute tragedy that we've lost someone of his calibre."

Mr Kelly's friend of more than 20 years Mike Andrews said he believed the weapon was a device used to shoot fishing tackle out beyond the waves.

Mr Andrews said Mr Kelly and an associate had tested the weapon and it proved to be faulty.

He said the weapon went off as Mr Kelly was unpacking it from the vehicle to fix.