Activity in China's service sector expanded at its slowest pace in two-and-a-half years in January, suggesting weaker demand during the first month of 2014, a private survey showed on Friday.

HSBC Holdings Plc released the Purchasing Managers' Index for services, which eased to 50.7 in January from 50.9 in December.

The official PMI for the service sector — calculated by the China Federation of Logistics and Purchasing and National Bureau of Statistics — was at a five-month low of 53.4 in January, down from 54.6 a month earlier.

For both PMIs, a reading above 50 indicates expansion.

Growth of new orders in the service sector slowed moderately as demand weakened last month, according to the HSBC data. The figures also indicate that service providers' costs rose at the start of the year.

The slower expansion of service activity in January reflected soft manufacturing growth and the impact of the government's latest measures to curb official extravagance, said Qu Hongbin, chief economist in China and co-head of Asian economic research at HSBC.

"As business sentiment remains stable, we expect service growth to bounce back a little in the coming months," he said.

"Yet a meaningful improvement relies on stronger growth of manufacturing and the implementation of reforms to boost the service sector."

The manufacturing PMI, released earlier by the NBS and CFLP, slid to 50.5 in January — the lowest level since August — compared with 51 in December and 51.4 in November.

The HSBC manufacturing PMI for January cooled to a six-month low of 49.5, a level indicating contraction, from 50.5 in December and 50.8 in November. It was the first time since August that the reading dropped below 50.

Other indicators, including industrial output, retail and fixed-asset investment, also weakened at the end of 2013.