Bay of Plenty and Rotorua residents are being urged to keep an eye on the weather, with MetService issuing a severe thunderstorm watch covering the region from midnight tonight until 11am on Saturday.

The watch includes Bay of Plenty, Rotorua, Waikato, Auckland, Northland and several other northern North Island districts, where thunderstorms could become severe as a band of unsettled weather moves across the country.

MetService said there is a moderate risk of severe thunderstorms developing, bringing intense downpours with rainfall rates of between 25mm and 40mm an hour.

Such heavy rain could trigger surface and flash flooding, particularly in low-lying areas, near rivers and streams, and in narrow valleys.

There is also a risk of slips and hazardous driving conditions caused by flooding and reduced visibility.

The warning comes as both cities experience cloudy conditions, with showers expected to develop this afternoon and potentially become heavy later in the day.

Temperatures are forecast to reach 22C, with light northerly winds developing through the afternoon.

MetService issued the watch at 10.25am on Friday and expects to provide its next update at 9pm.

People are advised to stay up to date with forecasts and be prepared for rapidly changing weather conditions overnight and into Saturday morning.