Major car crash on Auckland's Northern Motorway

The incident occurred at 5pm in the southbound lane of the Northern Motorway next to the Smales Farm bus depot. Photo / Kenneth Bate

A crash involving four or five cars has blocked multiple lanes on a motorway in Auckland this evening.

The incident occurred at 5pm in the southbound lane of the Northern Motorway next to the Smales Farm bus depot.

One man who witnessed the crash from the Northbound lane said it was a concrete truck that "smashed into about 5-6 cars then careened off itself".

A witness, who did not want to be named, said they were about 100 metres behind the crash when it happened. The person said it involved a large truck and trailer unit which swerved from either the fast or middle lane towards the left and finished up on the Northcote Rd off ramp. There was a silver BMW pinned under the trailer, the witness said.

Another witness said they were on the northern express bus going in the opposite direction when the crash happened.

"I didn't see the truck and the first car collide but I saw the car spinning out from impact. I saw the truck drifting across all of the lanes from the right-most lane to the left-most and into the barrier. It hit the second and third car as it was drifting across. Not sure if any more cars were hit, as we were driving past in the bus."

Police said all lanes are currently blocked as a result of incident.

Police and other emergency services are on their way to the scene and drivers are advised to avoid the area if possible.