Warrnambool's Stephen Bayard said he was driving his Mitsubishi hatch slowly down Viaduct Road about 11.15am on Thursday when a woman pedestrian told him there were flames coming from under his car.

He said he had never had a problem with the vehicle but he noticed the transmission service light was on this morning.

"The lady just walking along said there was smoke and flames coming from under the car, so I pulled over. I was only doing about 40km/h," he said.

"I went to flip the bonnet and there were flames everywhere.

"I got a real fright. It just went whoosh. A bloke came over and tried to put it out with an extinguisher but it was well alight."

Mr Bayard, who lives in south Warrnambool, said he had never had an issue with the car in the four years he had it.

"It's given me a fright. I've never seen anything go up so quick," he said.

Warrnambool police Senior Constable Aaron Toulmin said he was on patrol and was heading towards the breakwater when he saw the hatch on fire.

"We were in Viaduct Road just around the bend. We were on the scene before the call came through," he said.

"It was well alight when we pulled up. The fire brigade said there are no suspicious circumstances. It looks like the fire started in the front driver's side of the engine bay."