Shock after Dunedin Police catch 18 vehicles speeding in just over an hour.

Police were monitoring the stretch of the Southern Motorway between Dunedin and Mosgiel when they caught the drivers.

One car was clocked travelling at 165 kilometres an hour.

Brake NZ director, Caroline Perry, says that kind of speed is completely unnecessary.

"The impact, if you were involved in a crash at that kind of speed, would be huge and there is just absolutely no need for it."

Perry says driving that fast is risking lives.

"It's truly horrifying that, that many drivers are risking their own lives and the lives of other road users."

So far this year the country's road toll is 64, which is three up from the same time last year.