BEIJING - May saw a modest rise in China's service sector activity, with growth momentum easing further, survey results showed on Friday.

The Caixin China General Services PMI (Purchasing Managers' Index), produced by financial information service provider Markit and sponsored by Caixin Media, came in at 51.2 in May, down from 51.8 in April, in the slowest rate of expansion in three months.

A reading above 50 indicates expansion, while a reading below 50 represents contraction.

Firms' optimism towards this year's business outlook dipped to its lowest level in 2016 so far in May, the survey found, with an uncertain economic outlook weighing on business confidence.

Growth in business activity, new orders and employment all weakened from the previous month.

The Caixin China General Services PMI is based on data compiled from monthly replies to questionnaires sent to purchasing executives in over 400 companies.

Earlier in June, the official PMI for China's non-manufacturing sector (the service sector and the construction industry) came in at 53.1 for May, down from 53.5 in April and 53.8 in March, but well above the 50-mark that separates expansion and contraction. The data was jointly released by the National Bureau of Statistics and the China Federation of Logistics and Purchasing.

Businesses related to wholesale, retail, aviation transport, catering and software technology posted sound growth last month. However, road transport, residential services and repairing industries reported a drop in business volumes.