Police bosses have high-powered airguns in their sights and want to change the law so a licence is needed to own the potentially lethal weapons.

Briefing papers to Police Minister Judith Collins show the police want to reclassify any airgun with "muzzle energy in excess of 34 joules" as a firearm, meaning buyers would need a gun licence.

Some of the airguns in this category are estimated to be as powerful as a .22 rifle and can be bought over the counter without a licence by anyone older than 18.

Such weapons have been used in the alleged murder of undercover police officer Don Wilkinson, as well as a number of other violent crimes around the country.

Obtained by the Weekend Herald under the Official Information Act, the documents contain clauses in the Arms Amendment Bill that police believe would "address issues that have emerged" since the Arms Act was changed in 1992.

However, an airgun expert says the "horse has already bolted" in regard to powerful air rifles and points out that the National Government ignored the same recommendation made by Sir Thomas Thorp in 1997.

A spokesman for the Police Minister said police were exploring options for gun ownership and sales but it was "premature" to talk about potential recommendations.

Detectives who spoke to the Weekend Herald said high-powered airguns were being used frequently in violent crimes, including aggravated robberies, car hijackings and even murder.

"There are two issues: the power and the look of the gun. Most people would not pick an airgun from a real rifle," said one high-ranking officer.

"We are seeing more of these weapons all the time."

Sergeant Don Wilkinson was fatally shot with an FX Monsoon air rifle, which with a price tag of around $2000 is at the elite end of the market.

At the moment, anyone 18 or older can buy an air rifle without a licence.

Gun dealer William Cleverdon, of Will's Fishing and Firearms on the North Shore, estimated the store sold 20 air rifles each week. Firing projectiles at more than 1000 feet per second, Mr Cleverdon said many airguns were as powerful as a .22 calibre rifle.

Requiring a firearms licence would affect airgun sales, but Mr Cleverdon said regulation would "weed out the idiots".

"These guns are firearms. We tell our customers to treat it as a gun, because it is a gun."

Andre Doyle, of the New Zealand Council for Licensed Firearms Owners, said the organisation "wholeheartedly" supported the proposed licence change.

"The airguns they're talking about are pretty damn powerful. They're not toys," said Mr Doyle.

"When the current legislation was drafted [in 1992], these things didn't exist. The advance of technology has created these problems."

But specialist airgun dealer Ron Young, who sold the FX Monsoon that allegedly killed Mr Wilkinson, says the "horse has bolted" on airgun controls.

"I warned the police, years ago, that these air rifles were on the market. I made suggestions to the Thorp report, but nothing happened. Now everyone is spitting tacks, but it's too late, there's thousands of these guns out there."

Retired judge Sir Thomas Thorp conducted an independent inquiry into gun control at the request of former Police Minister Jack Elder. His 1997 report recommended that high-powered air rifles be classified as firearms.