The car hit a power pole on State Highway 88 near St Leonards Dr about 1.30pm, a police spokesman said.
The two occupants of the car escaped uninjured.
The road was closed after the car was engulfed in flames.
Ryan Henry was coming around a bend when he saw a truck driver helping two women out of the car.
"They’d just slammed in as I came around the corner.
Mr Henry only realised the extent of the crash when he got closer.
"The engine was sort of U-shaped around the pole.
"The ladies were just out of the car, which was pretty lucky because that’s when I spotted the flames out under the bonnet.
"Probably within a minute, she was up in fire and, within two minutes, it was fully engulfed."
Mr Henry thought the women were in shock.
He said the women appeared fine, but one was complaining of sore legs.
A Fire and Emergency New Zealand spokesman said crews from Willowbank and Port Chalmers attended the crash.
The crews asked for assistance from a water tanker because the vehicle was a hybrid, which required more water to extinguish.
A fire investigator was notified but did not attend the scene.
The crews extinguished the blaze and left the scene at 3.45pm.
