Chinese buyers have been motivated by price cuts at many dealers and rumors some cities will tighten controls on new vehicle ownership to curb traffic and smog, Zhang said.
The Beijing city government said last week it was considering fighting congestion by charging drivers to enter the Chinese capital's central district. Other cities have imposed quotas on new vehicle registrations.
Total Chinese vehicle sales, including trucks and buses, rose 10.3 percent over August last year to 1.65 million units.
General Motors Co. said earlier that August sales of GM-brand vehicles by the company and its Chinese partners rose 11.2 percent to 245,799.
Also in August, Japanese automakers extended their recovery from a slump last year when tensions between Beijing and Tokyo over disputed islands in the East China Sea kept buyers away from showrooms.
Japan's Nissan Motor Co. said sales gained 1 percent over last August to 86,000 units. That compared with a 6.3 percent decline for the first eight months of the year.
Toyota Motor Co. said sales nearly doubled, rising 95.8 percent to 72,100 units.
Germany's BMW AG said sales in China rose 34.6 percent to 34,166.