US carmakers have been under pressure from foreign rivals

Asian firms Toyota, Nissan and Honda enjoyed a better month, further eroding the market share of their US rivals.

Ford and GM lured consumers with discounts over the summer, but the promotions have lost their appeal.

Total vehicle sales at Ford were down almost 20% in September, while at GM they dipped by 24% overall.

The biggest drop was in sales of fuel guzzling sports utility vehicles (SUVs).

Strongest months

Many US consumers seem to be turning away from SUVs and trucks in favour of more efficient, less polluting vehicles.

Ford said sales of its Explorer, the best-selling SUV in the US, dropped by almost two thirds in September.

Total truck sales at Ford dropped by half, while at GM the picture was little better. SUV and truck sales at GM fell by 30% in September.

"There is legitimate pressure on some utility categories," said Paul Ballew, GM's executive director of global market and industry analysis.

However, Mr Ballew countered that the drop off came after months of growth.

"We're coming off the three strongest months in the history of the industry," he explained.

Ford said that it expected SUV sales to remain weak in coming months.

Better times

It was not all bad news for US producers, and the North American division of DaimlerChrysler reported a 4% increase in total sales during September.

Himanshu Patel, an analyst at investment bank JP Morgan, said that the drop in sales was due to a "pay back" effect following the strong performance earlier in the summer driven by discounts.

Asian companies are doing better. However, even they saw a drop in demand for SUVs and trucks.

Total sales at Toyota rose 10% in September. Car sales increased by 22%, but truck sales fell 4%.