The Caixin General China Manufacturing Purchasing Managers' Index (PMI), an indicator of manufacturing activity, edged down to 49.4 in April, a private survey showed on Tuesday.

The reading was fractionally down from 49.7 in March, signalling marginal deterioration in operating conditions, 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.

The data came on the heels of the official PMI that showed manufacturing activity expanded for the second month in a row in April.

The official PMI came in at 50.1 last month, slightly down from March's 50.2 but staying in the expansionary mode for a second month, according to data released by the National Bureau of Statistics (NBS) and the China Federation of Logistics and Purchasing on Sunday.

The official PMI samples 3,000 relatively large enterprises in China. The Caixin PMI samples 420 small and medium-sized manufacturing enterprises and is relatively volatile due to its small sample size and the dominance of small enterprises.