Northpower lines staff are working to restore power to about 4500 homes and businesses around Whangarei after an explosion at its 33,000KV station at Maungatapere.

Spokesman Steve MacMillan said the explosion happened about 11.30am and is believed to have been caused by bird strike.

It immediately cut power to thousands of homes and businesses in the Maungatapere, Poroti, Kioraroa Rd and Whangarei South area, including part of the CBD.

Mr MacMillan said many of the cut off properties had power reinstated within minutes, but work was ongoing and the rest should be reconnected shortly after 1pm.