Sports carmaker Porsche is taking the drastic step of replacing the engines in hundreds of range-topping Porsche 911 GT3 cars after fires destroyed two of the vehicles.

No one was injured in the separate blazes in Switzerland and Italy.

Porsche said the fires were caused by a faulty threaded connection in a conrod inside the engine block.

The connection broke loose, damaging the crankcase and allowing oil to escape and ignite.

Conrods or connecting rods join the crankshaft with the pistons.

Porsche earlier recalled all 785 cars so far delivered for checks and halted deliveries.

The affected cars will get a new 469-horsepower, 3.8-litre flat-six engine.

“I understand only too well how frustrating it can be when you have a great car in the garage which you are not supposed to drive,” Porsche boss Matthias Mueller told Germany’s Auto Motor und Sport magazine.

“I can also understand why customers are disgruntled but safety is not something you can compromise on.”

The model went on sale in Germany in August 2013.

The 2014 model was fitted with a modification which prevents the damage.

Replacing the entire engine of a high-end sports car is an unusual step.

Experts said it shows the premium maker is taking great care not to upset well-heeled customers.

The GT3 is one of the most expensive Porsche 911 variants and sells in Germany from 137,000 euros ($A204,720).

DPA