There was an explosion in car sales in 2009 thanks to massive policy support as the country overtook the US to become the world's largest auto market.

China sold 1.41 million passengers in June, up 23 percent from a year earlier.

Yet sales have witnessed a downward trend for three consecutive months, with June sales declining 1.83 percent from May.

The year-on-year growth rate from January to June hovered just under 50 percent, low compared with 84 percent in the January-February period.

Xiong Chuanlin, deputy secretary general of CAAM, attributed the decline to seasonal factors, saying the development of China's auto market "has returned to a sustainable speed" and that there is normally a slowdown this time of year.

"And a low comparison base also contributed to extremely high year-on-year increase earlier this year. Growth rate above 40 percent is not sustainable. We're keeping our sales projection for the yearly increase at 11 percent to 17 percent," said Xiong Friday.

Xiong said that there was less overtime at car factories this year compared with 2009, another sign that sales are slowing.

"On the whole, first half year sales performance is better than full-year sales of 2007, and almost on part with 2008," said Xiong.