Sergeant John Hamilton of Rangiora Highway Patrol said Tasers were designed to go on a belt and quick access was critical.
"You can't call time out, go to your car safe, fiddle with keys, and re-engage the person - it's not how it works," he said.
"One of the highest risk things an officer can do is knock on someone's door or pull over a car because you just don't know what that person is going to be like."
Senior staff ordered the cabin safe upgrade last year after it was discovered they could be prised open without a key.
While the safes - which are designed to give officers quick access to their Glock pistols and Tasers - were upgraded, the weapons have been stored in a locked safe in the boot of their cars.
In Canterbury however, area commander Superintendent Gary Knowles authorised officers temporarily to carry Tasers as sidearms.
They'll be back to normal procedure of being locked in the safes by next month once the upgrades are completed and police have no plans to change their current policy.
"The decision to allow Tasers to be worn was made for operational reasons to ensure the safety of response staff, and ensure that they retained the ability to deploy appropriate tactical options during the period when cabin safes were not available," Mr Knowles said.
The arrangement only applied to frontline response staff, and "only a very limited number" were carrying Tasers at any one time, he added.
Police association vice-president Luke Shadbolt said he wanted it made a fulltime move across the country.
He said carrying Tasers can give officers options to deal with escalating situations.
"At the moment when they're locked in the boot of your car, you don't have that immediate access to them," he told Radio New Zealand.
Police policy allows for Tasers to be carried on the belt "in certain situations for specific periods" and if operational requirements demand it.
Last year New Zealand police said they were looking to introduce a double-shot Taser that fires two high-powered charges without officers having to reload after several incidents in which the older model failed to work on armed suspects.