BEIJING, Dec 31 (Reuters) - Growth in China’s manufacturing sector slowed slightly in December as a crackdown on air pollution and a cooling property market weigh on the world’s second-largest economy.

The official Purchasing Managers’ Index (PMI) released on Sunday dipped to 51.6 in December, compared with 51.8 in November. But it remained comfortably above the 50-point mark that separates growth from contraction on a monthly basis.

Analysts surveyed by Reuters had forecast the reading would ease to 51.6 after unexpectedly picking up last month.

Boosted by government infrastructure spending, a resilient property market and unexpected strength in exports, China’s manufacturing and industrial firms helped the economy post better-than-expected growth of 6.9 percent through the first nine months of this year.

But November economic data disappointed analysts, with industrial output, investment and the property market all backing expectations that growth momentum is starting to moderate. (Reporting by Ben Blanchard; Editing by Kim Coghill)