A policeman's speed gun went into overdrive as a driver was clocked at 207km/h just north of Timaru.
Senior Constable Alister Doonan said he was parked on the side of Seadown Rd when he spotted a Nissan Skyline hurtling along, about 3.15pm on Saturday.
"I saw him coming and I knew he was going for it," Mr Doonan said.
"But I wouldn't have picked him at this speed."
Mr Doonan said the radar locked in on the Nissan and recorded the incredible figure - more than twice as fast the road's 100km/h limit.
It was the fastest speed the veteran of more than 30 years had recorded. The previous highest was 196 km/h and he also recalled a few drivers in the 170km/h range.
Mr Doonan said Saturday's incident happened on a flat section of a regional road where he often parked with the speed gun.
The driver pulled over, Mr Doonan said. There were two passengers in the car, but neither had the correct licence to take the wheel.
So he followed him home and handed him a 28-day suspension of his driving licence.
A 21-year-old local man will appear in the Timaru District Court next week on one charge of driving at a dangerous speed. He faces a minimum six-month ban from getting behind the wheel.