Automakers reported Tuesday mixed US sales in September, with General Motors's sales down sharply from a year ago.

GM, the largest US automaker, said it had delivered 187,195 vehicles in the United States in September, down 11 percent year-over-year.

Ford Motor, the number-two US automaker, said it had its best September since 2006, with sales up six percent from a year ago to 185,146.

Chrysler, the smallest of Detroit's Big Three and controlled by Italian group Fiat, reported a one percent rise in sales to 143,017 vehicles, pointing to its strongest September in a decade.

Japanese rival Toyota said it sold 4.3 percent fewer vehicles in the US compared with September 2012, at 164,457.

Analysts at Kelley Blue Book had predicted that overall September new-vehicle sales would fall in the first year-over-year drop since May 2011, in part because of two fewer sales days in the month and the fact that Labor Day holiday sales were included in the August numbers.

GM said it was optimistic about its sales outlook, despite the year-over-year September decline.

"We held our own when it comes to retail market share this month thanks to strong new products, including the Chevrolet Impala, Buick Encore, GMC Sierra and the Cadillac ATS and XTS," said Kurt McNeil, GM vice president of US sales operations.

"We expect a strong finish to the year and more growth in 2014 thanks to new products and a healthier economy."

Edmunds.com analyst Jessica Caldwell noted that Chevrolet dealers received their first shipments of the highly anticipated Corvette Stingray and inventory was growing for the new 2014 trucks.

"GM is certainly giving consumers diverse reasons to check out its current offerings," she said.

Shares in GM were flat in late-morning trade in New York, while Ford surged 2.3 percent.