James Shaw said there had already been category five storms that would have been given a higher rating if one was available.
A category five cyclone, as defined by New Zealand's MetService, has winds speeds between 215 and 230 kilometres per hour.
This differs from category five cyclones in Australia, which have winds exceeding 280 kilometres per hour.
Mr Shaw's comments at the Pacific Climate Conference in Wellington come as some New Zealanders affected by Cyclone Gita have been told it could take up to a year to clean up the region.
The storm devastated Pacific islands including Tonga and Fiji, before dumping large amounts of rain on New Zealand.
Cyclone Gita damaged or destroyed about 1,400 homes in Tonga.
Mr Shaw said scientists were linking extreme weather events to climate change and the stronger cyclones were challenging weather classifications.
One such storm was category five Cyclone Winston, the strongest cyclone on record, which killed dozens of people in Fiji in 2016.
"MetService experts tell me that it had much stronger winds than the 230 kilometre per hour upper-limit of a category five cyclone," he said, according to Radio New Zealand.
"The only reason it wasn't a category six cyclone is because we don't have a category six, but we might need one in the future."
Photo file Category 5 Cyclone Winston