A very active widespread area of thunderstorms is currently crossing the upper North Island, affecting Auckland, Waikato and Northland, some with continous rolling thunder - like in Auckland's west.

The front is connected to a change in wind directions, from nor'west to west and is the precursor to a cold change coming in to the South Island tonight and tomorrow.

WeatherWatch.co.nz says there have been hundreds of lightning flashes in the past hour and people should remain indoors if thunderstorms are nearby.

Heavy downpours may also cause pockets of flooding.

Thunderstorms are the most dangerous form of weather.

Flight delays are highly possible due to ground crew unable to work outside in electrical events.

View New Zealand's only Live and Free Lightning Tracker here (or in our Free App). www.weatherwatch.co.nz/lightning