In June alone, sales rose 5.2 per cent year-on-year to 1.85 million vehicles, the China Association of Automobile Manufacturers said in a statement, down from May's 8.5 per cent increase.
For passenger cars alone, total sales rose 11.2 per cent on the year to 9.63 million in the first half and 11.5 per cent to 1.56 million in June, the association said.
China has become critically important to foreign carmakers, given the size of the market and weak sales elsewhere in the world.
US auto firm General Motors said this week that it registered record Chinese sales during the first half and in June.
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Its sales in China in the first six months of 2014 increased 10.5 per cent from the same period last year to 1.73 million units, according to a statement. GM's China sales rose 9.1 per cent to 257,798 units in June.
"We anticipate sales remaining strong through the end of 2014, as more people -- particularly outside China's major cities -- become first-time vehicle buyers," GM China president Matt Tsien said in the statement.