China's auto sales growth tumbled to 3.7 percent in August, adding to a deepening economic slowdown, data showed Monday.

Customers bought 1.23 million cars, according to a government-authorized industry group, the China Association of Auto Manufacturers. The lower growth extended a steady decline from July's 11 percent rate and June's 15.8 percent.

The slowdown is a blow to a global auto industry that is looking to China, the biggest market by number of vehicles sold, to drive sales growth amid weak demand in U.S. and European markets.

General Motors Co., Ford Motor Co. and other global brands say their sales are growing faster than the overall market. That is squeezing smaller Chinese brands.

Growth in total vehicle sales also slowed in August, CAAM said. Sales rose 7.8 percent to 1.5 million units, down from July's 8 percent.

Sales were unexpectedly strong and might have received a temporary boost from sale prices, said Zhang Xin, an industry analyst at Guotai Jun'an Securities in Beijing.

"I think the main reason is 'On Sale,' especially led by the famous and luxury brands," Zhang said.

Zhang said buyers also might have been prompted to move up purchases to beat the imposition of curbs on new registrations in a growing number of cities to fight smog and traffic.

GM said earlier sales of GM brand cars by the company and its Chinese partners rose 7.3 percent in August from a year ago to 220,996 units, a new record for that month.

Germany's Daimler AG said sales of its Mercedes-Benz, smart, AMG and Maybach cars in China rose 5 percent in August to 14,840.

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AP researcher Fu Ting contributed from Shanghai.