Police have welcomed a law change which means people must have a firearms license to own the type of air rifle used to murder police undercover officer Sergeant Don Wilkinson.

The law change comes after the Government moved to reclassify pre-charged pneumatic (PCP) air rifles after they were used in the Auckland murders of Mr Wilkinson in 2008 and Keith Kahi in July this year.

Police national coordinator of firearms control, Inspector Joe Green said the law change meant police would have better control over who had access to the rifles which were "capable of causing serious injury or death".

"Classifying these air rifles as specially dangerous will ensure that the airguns that can cause the greatest harm, and those that are generally sought by the criminal community, are subject to the firearms licensing regime," Mr Green said.

The law change reflected the extent to which airgun technology has advanced over the last 15 years and meant owners had to be fit and proper persons before they could own a PCP air rifle, he said.

Owners would also be required to have minimum storage arrangements and complete safety training.

Owners of air rifles affected by the change have three months, until January 14, to get a firearms licence.

Don Wilkinson was murdered during a night-time police surveillance operation in Mangere in September 2008.

Mr Kahi was shot dead in the suburb of Botany Downs in July.