A senior Rotorua policeman has blamed Mongrel Mob leaders for an upsurge in crime after the discovery of a big arms cache.

More than 15 rifles, sawn-off shotguns and a pistol were found on Wednesday when police raided a house allegedly connected to the gang. In a separate raid, police found chemicals for making P, a home-made bomb and a shotgun. Five gang members were arrested in the raids.

Senior Sergeant Dennis Murphy said gang bosses had been recruiting members in Rotorua and were feeding prospects pure methamphetamine as payment for crime.

He vowed to crack down hard on the gang, saying there had been a marked increase in theft, burglary and gun-related offences since the release of several Mob leaders from prison in recent years.

"Since their release, we've noticed they've recruited young people and juveniles," he said. "We are seeing an upsurge in crime committed by these prospects and associates."

P was a key part of the recruitment.

"They are feeding young people methamphetamine and paying them for crimes they commit with methamphetamine and using that as a method to recruit young gang prospects."

The Mongrel Mob was not the only gang active in Rotorua, but it would continue to be targeted following recent incidents involving members and associates. Those incidents included a party on March 3 during which shots were reportedly fired by two Mob prospects, one aged 14.

The boy is being dealt with by the police youth aid section, while a 20-year-old man has admitted possessing a pistol and is to be sentenced in May.

Detective Sergeant Garry Hawkins of Rotorua's criminal investigation branch said it was a major concern having young "gang wannabes" on the streets with firearms.

"They just think it's cool to run around with guns," he said. "We want to nip it in the bud before someone gets shot."

He said all gangs, not just the Mongrel Mob, were to blame for encouraging the behaviour.

"They are a faction of our society that live by a code of violence."

Youth involvement in gangs was not unique to Rotorua, and it had serious consequences for those involved.

"They'll end up doing life by instalments," Mr Hawkins said.

It is not known whether the guns seized yesterday are among more than 20 shotguns, rifles and airguns stolen from a sports store in Rotorua on February 2. Mr Murphy said the store owner would be asked to look at the guns to see if any were those that had been taken.