Activity in China's services sector — the biggest contributor to gross domestic product — expanded at its slowest pace in 17 months in December, according to a closely-watched private survey, an indication of headwinds faced by China in its shift toward a more service-oriented economy.

The Caixin/Markit Purchasing Managers' Index (PMI) for December fell to 50.2, from November's 51.2. In October, the index hit a three-month high of 52. December's services PMI reading was the lowest since July 2014.