Images from the scene show a white car lying on its side with a smashed windscreen and missing front bumper.
Chain-link fencing alongside the cycleway appeared heavily damaged, with two support posts bent over.
A police cordon was in place at either end of the crash site.
Hato Hone St John said two ambulances went to the crash site and one patient in a serious condition was transported to Auckland City Hospital.
Police have been approached for comment.