A Christchurch tenant who left behind an air rifle in his vacated rental later sent armed police swarming on his landlord's property by reporting the firearm stolen.

According to a recent Tenancy Tribunal decision, the incident started two days after the Christchurch mosque shootings when the tenant moved out of his New Brighton rental and was found to have damaged its walls, kitchen bench, mattress and microwave.

He also left an unlicensed air rifle under the bed.

The tenant - who the Herald have chosen not to name because he is under 18 years old - has since contacted the Herald to say they weren't able to attend the Tenancy Tribunal hearing and that they dispute many of the landlord's claims.

According to Tenancy Tribunal decision, however, landlord Alan Butcher found the rifle two weeks later and called police and handed it over to them, before telling his tenant what he'd done.

That led the tenant to phone police and claim Butcher had stolen his firearm - a call that sent armed police swarming on Butcher's premises.

Faced with armed officers, Butcher was forced to explain what had happened and the police eventually confirmed they already had the rifle in custody.

"It was a big shock for Mr Butcher to find the air rifle and he then had to deal with

the police twice over it," the Tenancy Tribunal adjudicator said.

"The second time armed police came to the premises ... was at a time of extremely heightened tension over the possession of firearms."

The adjudicator found the tenant showed a disregard for the difficult situation he put his former landlord in.

He also found the tenant had committed an unlawful act by keeping the unlicensed firearm in the house and awarded $300 in exemplary damages to Butcher.

"It is obviously behaviour that the Tribunal should discourage because it is not in anyone's interests," he said.

The tenant also had to pay a further $541 to cover the repairs and cleaning needed at the tenancy after he vacated.

The tenant later told the Herald he was overseas at the time of the tribunal hearing because he mistook the date it was being held.

He said he only damaged the flat's kitchen bench by leaving a burn mark on it, damage that he immediately told the landlord about.

He also claimed the landlord unlawfully entered his flat and removed the air rifle before his tenancy ended, not after he vacated the flat.

He said he had mostly cleared his belongings from the flat but hadn't fully removed his them.

His father then called police to ask them to recover the air rifle, he said.

This led to two armed police visiting the landlord.

The tenant also claimed this took place almost two months before the Christchurch mosque shootings, not days after it as the Tenancy Tribunal decision stated.