He and another man - possibly a member of the public - then "half-carried, half-dragged a woman kicking and screaming across the road to the police car", she said.
Traffic on the motorway was almost at a standstill before the crash site, she said.
Police confirmed they were attending an incident near the Greenlane overbridge.
"The right-hand lane is currently blocked causing significant delays and we advise motorists to avoid the area if possible," a spokesperson said.
"Further information will be available as it comes to hand."
A second accident on the Southern Motorway near the Karangahape Rd overbridge has also slowed traffic heading south.