A man is been fighting for his life overnight after a tree crashed down on a car on Auckland's Southern Motorway during a fierce storm overnight.

Gusts of wind up to 100km/h brought power lines down in various parts of the city, leaving thousands without electricity, while some road accidents were blamed on the storm.

There were six other people in the car at the time of the accident, though a member of the public pulled all seven of them out.

The critically injured man is in his 40s, while two others had moderate injuries. 

There was a power outage at the time, which meant there were no lights on the motorway.

Forecasters had been predicting some more rough conditions after a "weather bomb" last week that was damaging in many parts of the country, causing flash flooding and closing off roads due to slips.

In the north of the country, emergency services were kept busy by more than 150 weather-related callouts - downed power lines, trees blown over, and runaway trampolines.