Lightning lit up the early morning sky for people heading to work around 6.30am in the Bay of Plenty this morning.

Rain is forecast to develop this morning, with possible possible squally thunderstorms and hail.

There is no official thunderstorm watch in place for the Bay of Plenty, but there is one in force for the Waikato region.

"There is an active front is moving over the upper North Island early this morning with embedded thunderstorms. A few of these thunderstorms may be severe bringing brief heavy rain, hail and squally wind gusts," says the MetService.

"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips.

"Squally winds may cause some structural damage, including damage to trees and power lines, and make driving hazardous.

"A Severe Thunderstorm Watch means conditions are favourable for severe thunderstorms in and close to the watch area.

"People in these areas should be on the lookout for threatening weather conditions and monitor for possible Severe Thunderstorm Warnings."