About 1,340 properties have been hit by a power outage on Auckland's North Shore this afternoon.

The outage is in the Birkdale area but the cause is yet to be determined.

"We were alerted to the outage by a member of the public about 4.30pm and crews are on the way to deal with it," Sandy Hodge, spokeswoman for Vector, said.

"At present it is estimated the power will be restored by about 7pm or earlier."