Weather: Vicious thunderstorms, strong gusts to strike North Island, tornadoes possible

Parts of the North Island are set to be lashed by thunder, strong winds and possible tornadoes on Thursday night.

Metservice has issued a Severe Thunderstorm Watch for northern areas of the North Island for Thursday night into Friday morning.

The NZ Transport Agency (NZTA) is urging motorists to slow down.

"Keep your lights on and maintain a safe following distance," NZTA said on Twitter.

"Extra caution is also advised on the Auckland Harbour Bridge due to strong wind gusts."

Meteorologist Lewis Ferris warned that gusts could hit 110km/h.

"We are advising residents in affected areas to tie down objects that could be caught by the wind overnight," he said in a statement.

"There is also a possibility of tornadoes developing with the severe thunderstorm cells".

Vector says it is monitoring the weather and has crews ready for any power outages.

"The risk of trees coming into contact with power lines and cars colliding with power poles in the wet, increases during these types of weather events," Vector's head of network field services, Marko Simunac, said.

If any power lines come down, Vector will remotely shut down power to that area as a safety precaution.

Metservice said the warning came as a "complex low-pressure system" ripped its way across New Zealand on Thursday. 

Auckland has been battered by heavy rain and at least 50 lightning strikes, according to NIWA. Photos on social media show some stores at Sylvia Park mall have flooded.

More "heavy rain, squally thunderstorms, strong winds and possible tornadoes" should be expected on Friday for the north, according to Metservice. The South Island could also see some thunderstorm activity, with the West Coast most at risk.