Once person has been injured in a crash on Auckland's Northern Motorway this afternoon.

The crash happened just after noon at the Esmonde Rd offramp and blocked two of the three citybound lanes for about half an hour.

Traffic cameras show congestion building before the Northcote Rd exit, 1.5km north of the crash.

An ambulance spokesman said one person was taken by ambulance to North Shore Hospital with moderate injuries.