Watch: Shocking moment speeding driver smashes into cars on Auckland motorway

Shocking dashcam footage shows a speeding driver smashing into multiple cars on an Auckland motorway on Monday afternoon.

Ben Comemadang was driving home from work on the Southern Motorway, when his dashcam caught a driver speeding past before smashing into the back of a white Mazda. The car then careened across lanes, hitting multiple other cars.

He told Newshub it was terrifying to witness.

"The car was going well over 100 and at first looked like it was going to hit the back of the bus, but then it swooped to the side into the back of the SUV."

He said the SUV then spun out in front of the bus and ended up in a roadside bush, but the speedster kept driving.

"At least three cars were hit, the video shows two being crashed into, then the speeding car ended up in the bushes as well."

He said he pulled over to check on the driver and passenger of the white Mazda, who were both in shock.

"The passenger came out of the car and was shaking, in shock. Then I went to see the driver who was panicking and crying. I told her she'd better get out [of the car] because I smelled gas."

The driver of the white Mazda, Waduge Himesha Erandi Fernando, told Newshub the crash was one of the most terrifying things she's ever been involved in.

"It all happened so fast and I was in shock, I was literally shaking and couldn't think."

She said it felt like she was unconscious, but she could hear and see people trying to help her.

"People were trying to give us water and get me out of the car, they helped me to turn off the engine because there was a smell of gas."

Mr Comemadang said he saw the offender's car in the bushes about 20 metres ahead of the white Mazda, but decided not to go over.

"Someone was calling police and ambulance and my main aim was to check on the victims."

He said he left before police arrived as the scene started to get crowded.

Ms Fernando said she sustained a slight muscle tear in her right calf during the crash, as well as neck pains from the whiplash, but is lucky it wasn't worse.

"I would be very scared to drive again for a few weeks, I have never been involved in an accident before and I was doing everything right."

She said police called her last night and said the driver of the speeding car was still in hospital undergoing testing.

She said the driver had told police they did not remember anything about the incident.

Mr Comemadang said witnessing the crash made him much more wary of the dangers of being on the road.

"Life is so short, things like that can happen to you at any point. When I get home now I go straight to hug my daughter."

Newshub has contacted police for comment.

Newshub.