General Motors said Tuesday year-on-year sales fell for the second straight month in May, reflecting a slowdown in the world's largest auto market as authorities roll back stimulus measures.

The US giant's figures show sales fell 2.7 percent to 190,674 units from 196,004 in the same month last year and were down 6.2 percent from April.

April sales fell 4.6 percent year-on-year to 203,367.

China's auto market has become increasingly important to GM as demand weakens in the United States. China, where GM's international operations are now based, overtook America as the world's biggest auto market in 2009.

Despite the recent falls, the auto maker said in a statement that for the first five months of this year sales cruised past one million units, hitting a record 1.1 million.

Its sales in China last year increased 28.8 percent year-on-year to an annual record 2.35 million vehicles, outstripping its home market.

For the whole industry auto sales in China rose more than 32 percent in 2010 to 18.06 million units, according to the semi-official China Association of Automobile Manufacturers (CAAM).

But growth has slowed since the middle of last year as the government began withdrawing stimulus measures such as tax breaks for small engine vehicles aimed at cushioning the impact of the global economic downturn.

China's auto sales dipped 0.25 percent in April in their first on-year fall in more than two years, according to CAAM.