"I tried to see if anyone that was around before us were on the phone calling the police and I couldn't see anyone but this man standing filming everything that was happening."
She called the police as her partner tried to help the man who was trapped under his vehicle.
And police say a rise in number of people taking photos and recording videos are crash scenes is causing concern.
"Police have noticed an increase in the number of people taking photos or recording video at crash scenes and other events where emergency services are present," said a police spokeswoman.
"If the photos/video are then shared on social media, that could breach the privacy of the victim/s or other people present at the scene."
The spokeswoman said it could also lead to identification of a victim, such as when the vehicle's registration plate is shown, prior to police being able to carry out family notifications.
"The last thing we ever want is for someone to find out their loved one has been involved in a crash or other event via social media," she said.
"And there is a risk that graphic or inappropriate images could cause distress for people who view them, or further victimise those involved in the event."
Police said the man suffered head and arm injuries and had been transported to Wellington Hospital by helicopter. The three in the other car were taken to Hutt Hospital with moderate injuries.
"[My partner] said that the man recording went up to the window of the Toyota Surf and recorded the man who was trapped and wedged in the car and filmed his face and his car," said the witness.
"I felt there was no need and I felt really upset for the families of these people who are seriously hurt [that] someone is recording them in this state after such a horrific accident, it wasn't the time or place to be making what I felt was like a movie."
She has posted on Facebook: "To the man standing there recording the injured and distressed men involved, going up to there cars recording them rather then helping them was horrible to see. Cannot believe the amount of photos taken and all was disgusting. Awesome to see the people helping and keeping the flow of traffic though that was amazing!"
The Serious Crash Unit is investigating the accident.