One person has been taken to North Shore Hospital after a car flipped on the Northern Motorway this afternoon.

Emergency services were called to the crash just north of the Onewa Road off-ramp at 1.09pm.

A St John spokesperson said one person was serious and has been transported to North Shore Hospital.

"Two others were in a minor condition."

This motorist has been stuck in traffic for an hour before even getting on to the Harbour Bridge.

The NZ Transport Agency is advising motorists heading north to instead use the Western Ring Route (SH16 and SH18).

All four lanes of Auckland's Northern Motorway have now been open, but major routes are jammed as a result of the near two-hour closure.

Long tails are backed up on the Northern motorway northbound, and it's slow going on the Northwestern as motorists try to avoid State Highway One.

 

SH1 NORTHERN MWY, NORTHBOUND - CRASH - 1:15PM
A serious crash is blocking ALL LANES north after Onewa Rd. All traffic being diverted off the motorway at Onewa Rd. Avoid this route or expect diversions and delays. ^TP pic.twitter.com/Oblo5fwFzF

— NZTA Akld & Nthlnd (@NZTAAkl) August 21, 2018

North-bound traffic was being diverted off the motorway at Onewa Road and traffic is building up back across the Auckland Harbour Bridge.

There is a tail queue at Newmarket as well as queues southbound near the accident due to rubberneckers, according to Newstalk ZB's Time Saver Traffic.

The Serious Crash Unit is attending the incident.

More to come