Vehicles at a Hongqi car dealer in Beijing. - Car sales are falling in China this year but one brand is speeding ahead: The national 'Red Flag' sedan is flying high, powered by purchases from the government, state companies and patriotic citizens.

Auto sales in China fell 14 percent in November over the same month in 2017, the Chinese Association of Automobile Manufacturers said Tuesday.

Sales fell 14 percent compared with November 2017, continuing a downward trend that started in July. It is the largest decline so far this year, the association said in a press release.

"This is the first sustained downturn in memory," said Michael Dunne, CEO of ZoZoGo, a firm that advises automakers on doing business in China. "We would have to go back to the Asian financial crisis in 1998-1999 to see the last time China had flat or down sales for four months or more in a row."

A slowing economy, a crackdown on certain types of auto lending and a trade war with the United States have all been factors in contributing to the slowdown, Dunne said.

There were a couple of bright spots though. Heavy truck sales rose last month, which was surprising, Piper Jaffray analyst Alexander Potter said in a note published Tuesday. The growth came primarily from a jump in the sale of semi-trucks, which outsold construction trucks for the first time in more than a year.

WATCH: Elon Musk's big ambitions may be killing Tesla