The Serious Crash Unit is examining the scene, and the road remains closed.
St John said the service sent six vehicles to a “traffic incident” in Penrose at 2.05pm, including three ambulances.
Fire and Emergency New Zealand told the Herald that two fire trucks were assisting police at a motor vehicle crash in Penrose.
Jerry Wong of nearby New Moon Furniture told the Herald police blocked the road and the damaged vehicles were cleared from the scene.
Wong said he saw at least three ambulances and “a lot” of local policemen attend, describing the accident as “so scary”.
He claimed one of his customers had narrowly avoided being part of the crash by deciding not to take a U-turn on the street.
Another nearby business owner described a heavy emergency services presence following a “fairly significant” accident 50 metres from his store.
Inspector Peter Raynes said a Critical Incident Investigation has been launched and police have also referred the incident to the Independent Police Conduct Authority.