Business activity in China's service sector dropped slightly in April, a private survey showed on Thursday.

The Caixin China General Services PMI (Purchasing Managers' Index) came in at 51.8 in April, down from 52.2 in March, according to the survey conducted by financial information service provider Markit and sponsored by Caixin Media Co., Ltd.

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