Consumers seem more reluctant to make big purchases

The company said purchases of pick-up trucks and sports utility vehicles (SUVs) had helped its sales grow 5.3% against the same month a year ago.

Elsewhere, Ford saw sales fall 14.4% while Chrysler sold 6% fewer vehicles.

Industry analysts say rising mortgage payments and turmoil in the financial markets may have contributed to the ongoing sluggish market.

GM said its success had come despite a decline in sales to rental firms and "an overall market that remains challenging and competitive".

Asian competitors have been stealing a march on the US manufacturers, with Nissan reporting a 6.3% sales in August and Honda seeing car sales up 11.7%. However Toyota's sales fell 2.8%.

The vice president of GM North America, Mark LaNeve, said his firm was enjoying a growing reputation.

"The myth of import superiority is being destroyed," he said.

"In countless independent consumer surveys, blogs and expert reviews, it is becoming increasingly evident that we build the highest quality vehicles and deliver them with world-class service."

Ford's continued losses come amid a radical restructuring plan that will see 16 factories close by 2012. It has sold the Aston Martin marque and is also talking to potential buyers of both Jaguar and Land Rover as it tries to get to grips with more competitive and successful Japanese rivals.

US vehicle sales will be 350,000 fewer than last year according to CSM Worldwide - at its lowest level since 1998.