Chief Fire Officer Bill Hutchinson said firefighters discovered that the appliance had no brakes when they went to move it out of the car yard on Monday morning. Otherwise they wouldn't have found out until the next call, which was to a fire at 3.30am on Tuesday.
Those who could have suffered most were those who needed the brigade in an emergency, he said. If one of Kaikohe's fire engines was out of action another brigade would have to respond from further afield, delaying arrival by half an hour.
In the previous week the brigade had responded to about 15 alarms, three of which involved fatalities.
The vandal had also put the firefighters, and other road users, at risk by disabling the brakes.
It was a deliberate act that required someone to crawl under the vehicle -- "It's not like someone's just walked past and slashed a tyre" -- and came at a time when the brigade was stretched and needed more volunteers," Mr Hutchinson added.
The appliance has been repaired, and police are investigating.