(Adds quotes, context)
BEIJING, Sept 11 (Reuters) - China's automobile sales fell 3.8 percent in August from a year earlier to 2.1 million vehicles as a weak macro economy and trade frictions with the United States made consumers cautious about spending, an industry association said on Tuesday.
Last month's sales drop follows a 4.0 percent fall in sales volume in July and an increase of 4.8 percent in June.
The two consecutive months of weakness reverses a sales uptrend since February when sales volume fell 11.1 percent.
Overall sales for the first eight months of the year totalled 18.1 million vehicles, up 3.5 percent from the same period a year earlier.
Worries about China's overall economic situation led people to tighten their purse strings during July and August, said Xu Haidong, an assistant secretary general of the China Association of Automobile Manufacturers (CAAM).
China's on-going trade spat with the United States was less of a factor, but it did weigh on consumer sentiment, Xu added.
"The trade frictions brought uncertainties, impacted sentiment and made Chinese customers more cautious," Xu told reporters.
CAAM attributed weak sales of American brands to product and marketing issues, and Xu noted that there was no boycott of U.S. auto brands.
Citing Ford Motor Co as an example, Xu said Ford is not rolling out new or redesigned products fast enough and has allowed Chinese consumers to turn to other brands.
CAAM on Tuesday kept its forecast for the year unchanged.
The association forecast overall market growth of 3 percent this year, in line with the previous year but significantly below the 13.7 percent gain in 2016.
Sales of new-energy vehicles a category comprising electric battery cars and plug-in electric hybrid vehicles rose 49.5 percent in August from a year earlier to 101,000 vehicles.
That took new-energy vehicle sales in the first eight months of this year to 601,000 vehicles, up 88 percent from the same period a year earlier. (Reporting by Lusha Zhang and Norihiko Shirouzu; Editing by Sunil Nair)