The offending driver, a 22-year-old man from Craigieburn, was negotiating a sweeping downhill bend of the Princes Highway near McKinnons Bridge about 5.30pm Saturday.

Senior Constable Troy Wearne of Terang said the off-duty officer and another driver travelling east had to veer to the other side to avoid a collision.

"It was nearly a head-on," he said.

"The oncoming driver appeared to have lost control and went onto the wrong side of the road.

"We have interviewed the driver and are appealing for witnesses."

Meanwhile, Hamilton police are puzzled by a smashed wall at a public toilet block in Mitchell Park Hamilton and believe it may have been rammed in a hit-run incident. 

No debris from the vehicle was left at the scene when officers arrived yesterday morning to investigate.

"We believe a vehicle was involved because of the extensive damage to an end wall - it was stoved in," Sergeant Rex Habel said.

"There's at least $2000 damage.

"It adjoins the St Marys Cricket Club ground. "If members of the public has information that could help us they should contact the police station." pcollins@fairfaxmedia.com.au