General Motors has reported an 18 per cent jump in its US sales in August despite recent market turmoil, and expressed cautious optimism about the US economy.

'Our portfolio of trucks and vehicles like the Chevrolet Cruze, Chevrolet Equinox and GMC Terrain, are helping us gain market share, which has increased in seven of the past eight months,' vice-president for US sales Don Johnson said.

Retail sales boosted deliveries to 218,479 vehicles last month.

GM said it is 'monitoring consumer sentiment and other economic indicators' but has not changed its forecast for 2011 sales in the 'low end' of about 13.5 million vehicles.