BEIJING - The purchasing managers' index (PMI) for China's non-manufacturing sector came in at 53.7 in September, down from 53.8 in August but still in the expansion zone, the National Bureau of Statistics (NBS) said Monday.

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

A breakdown showed the service sector activity accelerated slightly, with the sub-index for the sector up to 53 from 52.5 in the previous month. Rapid expansion was seen in industries such as airlines, postal services, telecommunications and software, and monetary and financial services, with their sub-readings staying above 58.

The sub-index for the construction sector fell to 57.6 in September from 61.2 in August but remained on a relatively high level, according to the NBS.

The sub-index for business expectation fell to 59.7 in September from 60.4, still in the expansion zone, showing that non-manufacturing enterprises remained optimistic about future market developments, the NBS said in a statement.

Monday's data also showed that China's manufacturing PMI firmed up to 49.8 in September from 49.5 in August.