HSBC's monthly purchasing managers index for the services sector produced a reading of 50.7 in May, marking one of the slowest months in the survey's eight-year history.
The survey is compiled by sending questionnaires to around 400 private sector, non-manufacturing companies. A reading above 50 suggests growth, but this month's figure was lower than the 51.4 score in April.
"Anecdotal evidence suggested that tough market conditions weighed on services activity growth," the bank said.
The depressed view is a contrast to the state-sponsored survey published on Tuesday, which with a reading of 55.5 suggested the services sector accelerated at its fastest pace since November.
The official survey is wider and tends to track larger companies, many of which are backed by the state.
HSBC economist Qu Hongbin said the bank's survey showed an 11-month drop in the "business expectations" component, which fell from 60.7 to 58.1.
"Growth momentum remains slow and private sector sentiment is weak," he added.
We think policy makers should continue to ease monetary and fiscal policies in the coming months to help support growth.