Ford is being sued by Australian motorists who say their cars have unsafe transmissions, including a Perth woman whose vehicle caught fire.

The action will involve thousands of motorists, says Bannister Law, which has filed the class action.

The firm said it was acting on behalf of disgruntled owners of Ford Fiesta, Focus and EcoSport models equipped with the six-speed, double clutch Ford PowerShift transmission.

That would affect the owners of at least 60,000 cars.

One owner, Perth woman Kelly Richards, believed the transmission on her Fiesta caused an engine fire that destroyed her car.

The car had been in and out of the dealership for repairs since she bought it, wasn't driving properly and shuddering when accelerating before an independent mechanic identified the transmission as the problem, she said.

"Then my father-in-law was taking a short trip when the engine began to smoke," she said.

"Quite quickly, the entire front of the car was engulfed in flames.

"It was a frightening experience and the car was a write-off."

The reported problems are sudden accelerations without warning, difficulty in stopping while braking and the transmission slips, bucks, jerks, and harshly engages.

The systems had caused angst overseas, including the US where a class action has already been filed.

"The many accounts we've been gathering from owners of affected vehicles, suggest that these cars are not fit for purpose, they're not free of defects and, most worryingly, they are not safe," lawyer Charles Bannister said.

"These, we argue, are breaches of Australian consumer law."

The class action would seek full refunds and damages ensuing from repair costs, out of pocket expenses, and aggravated damages for stress, inconvenience and humiliation.

A Ford spokesman said while it was aware of the lawsuit, the company was yet to receive it and would not comment.