An Invercargill motorist may have saved lives, Police say, by reporting a speeding driver swerving through traffic on a busy State Highway.

The motorist called 111 to report a car going at least 50kmh over the open road limit, overtaking multiple vehicles and weaving in the lane as it drove north towards Gore on State Highway 1 around 11:10am on Saturday.

Constable Mel Isaacs was one of the Gore units dispatched, and she said she didn't have to wait long to spot the red Audi coming toward her.

And when the police car's radar locked on to the 18-year-old's car, it showed the speed was more than twice the open road limit.

"I didn't quite believe it when I saw the speed on the radar - I thought 'is that right?'."

But it was right.

It also turned out the 18-year-old behind the wheel is faster at driving than he is at learning; just last week, Constable Isaacs had pulled him over for going 30km/h above the 100km/h limit.

"When he pulled over for me this time, he was more concerned with the speed I had to do to catch up to him than anything he had done wrong.

"I've never seen a car doing the speeds he was, and if it went wrong, it would have been catastrophic.

"Unfortunately, there are some drivers who shrug at the road safety message, and that puts everyone around them at risk."

The teen now faces two charges of dangerous driving, relating to the speed and the manner of driving, and will be summonsed to appear in court.

His licence has been suspended for 28 days and the car was towed away.

"We're unapologetic about targeting speeding drivers.

"High-velocity crashes are horrific events to attend and we will do everything we can to prevent them.

"The motorist who called 111 today potentially saved lives by picking up the phone and giving us the chance to act.

"If you see dangerous driving on the road, please call 111 as soon as you can - don't assume someone else will make that call."

Reproduced with permission