BEIJING - China's service industry is expanding at the fastest pace for nearly six years, a private survey showed Monday.

The Caixin China General Services Business Activity Index, which mainly monitors small and medium-sized firms, rose to 54.7 last month, up from 53.9 in December. It was the highest reading since May 2012.

A number above 50 indicates expansion, while a figure below that points to contraction.

The private survey's results accord with the official observation of the service sector, which also increased in January.

January's upturn was mainly due to greater client demand, with new business growing at its quickest pace in 32 months, according to Caixin.

The expansion is more evident that the Chinese economy is off to a good start in 2018, according to Zhong Zhengsheng, director of macroeconomic analysis at CEBM Group, a subsidiary of Caixin Insight Group.

The Caixin China General Manufacturing Purchasing Managers' Index (PMI) came in at 51.5 last month, unchanged from that in last December, which was the highest reading since August.

Strength in both the manufacturing and services industries supported the Caixin China Composite Output Index, which covers both manufacturers and service providers, to jump to a seven-year high of 53.7 in January.

Downside risks remain due to signs of moderating demand for manufactured products and rising costs that weigh on service companies, Zhong warned.