Reports are coming in of a small tornado touching down near the Puhoi tunnel north of Auckland city.

The tornado appears to have been caught on camera and can be viewed via the Times FM Facebook page.

WeatherWatch.co.nz forecasters have advised Auckland Civil Defence that very unstable weather conditions over the upper North Island could generate isolated small tornadoes both today and tomorrow along with isolated thunderstorms.

In the past two hours very large clouds and heavy downpours have started to develop over northern Auckland and Northland.

Heavy showers, some with thunder, may also cause localised flash flooding.

The unstable weather conditions will last until the end of Thursday.