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.