A van has been flipped on the Northwestern Motorway near Massey.

Video of the incident shows the van on its side with emergency services in attendance.

NZ Transport Agency says the accident happened on city-bound lanes of the motorway around 11.50am.

The crash had reduced city-bound traffic to one lane through Massey, with delays expected.

All lanes have now reopened, but delays are expected while congestion eases.

A spokesperson said Hato Hone St John was notified at 11.42am.

Two people were assessed and treated at the scene but did not require transportation to hospital.

Police have been approached for comment.

More to come