A developing tropical cyclone could threaten New Zealand next week, a weather prediction website has warned.

WeatherWatch.co.nz head analyst Philip Duncan said computer models showed a tropical depression with potential to become a severe tropical cyclone forming north of New Zealand.

New Zealand, Vanuatu, New Caledonia and Fiji would be at risk from the system if it follows current modelling, he said.

"As with all tropical lows, it doesn't take much of a shift to spare New Zealand. We'll certainly be hoping for that, but considering we've had four named storms reach our country in just the past few weeks it wouldn't be out of the question for this to do the same."

The computer models, produced by ECMWF in Europe, show a large scale cyclone of potentially category 4 strength forming to the north of New Zealand and tracking south east.

Though it was possible the storm would miss New Zealand, the same models predicted the path and strength of Cylcone Yasi 10 days before it hit north Queensland on February 3, said Mr Duncan.

But Metservice weather ambassador Bob McDavitt said while a depression is forming, it was too early to tell whether it would threaten New Zealand.

A cyclone system simply "does not exist" at this stage, he said.

"It's so far away it could easily change and in fact it normally does."

New Zealand has been hit by tropical storms including cyclones Zelia, Vania and Wilma this summer.

NIWA is predicting another five or six tropical cyclones yet to form during cyclone season, which Metservice is predicting to end by May.

WeatherWatch.co.nz said the cyclone season is likely to run longer this year because of strong La Nina conditions raising water temperatures in the Pacific Ocean.