A police officer was injured during the incident on the Northern Motorway.
A man has been arrested after allegedly knocking out a police officer on an Auckland motorway.
Police were called to the Northern Motorway, near Tristram Ave, just before 10.30am after reports of a man jumping in front of traffic.
Three vehicles were involved in a minor crash as a result.
Police said the man reportedly threw himself at a truck.
"A police unit has attended and the man has jumped on to the windscreen of the police car and damaged it.
"The officer has [got] out of the vehicle where he has been assaulted by the offender and a struggle has ensued," police said.
The officer tried to Taser the man, but was knocked unconscious by the alleged offender.
Members of the public then got involved - restraining the offender until other police staff arrived.
The man was arrested at the scene.
The police officer has since been taken to hospital and assessed for his injuries.
"Police will be ensuring that they have welfare wrapped around them following this alarming incident," police said.
The alleged offender has also been taken to hospital as a precaution.
Inspector Peter Raynes described the incident as alarming.
He said inquiries are ongoing and charges are likely.
The 19-year-old was found in a remote area in the hills of Upper Hutt.