China's foreign exchange reserve shrank for a third straight month in September and by slightly more than markets expected. That's according to data released from the central bank on Friday.

The reserve -- the world's largest -- stood at 3.17 trillion US dollars in September, down by 18.79 billion dollars from August levels. Traders believe the central bank has since July stepped in to prop up the yuan, which weakened 2.7 percent against the dollar so far this year.

At the same time, tourists’ surging demand for foreign currencies during the National Day holiday, also contributed to the shrinking pool of forex reserves. As for the offshore yuan, it fell to a nine-month low against the dollar early on Friday. The yuan was included in the IMF's special drawing right basket on October 1st --leading to speculations the currency would appreciate.

But the dollar's recent strength on expectations of a Fed rate hike in December meant the offshore yuan softened instead. Authorities say China's economic growth rate remains robust.

Analysts are expecting onshore yuan to make up for the falls when markets reopen Monday.