The Fire Service it received 45 emergency calls as a direct result of fireworks on Friday, two of which were serious incidents.
In the Auckland suburb of Half Moon Bay, scrub caught alight and threatened homes.
In Rotorua, fireworks landed on the roof of a single-storey house, starting a fire in the ceiling cavity.
Fire crews brought the blaze under control fairly quickly but the property was badly affected by smoke.
The Fire Service says bad weather in Wellington and Christchurch may have curbed fireworks-related problems.
Christchurch event postponed
The weather forced Christchurch's Guy Fawkes Day fireworks to be postponed on Friday.
The Christchurch City Council says the event will now be held at New Brighton Pier on Saturday night.
The display usually attracts 80,000 people.