The preliminary Caixin China manufacturing purchasing managers' index (PMI) fell to a six-and-a-half-year low of 47.0 in September, below the 47.5 forecast in a Reuters poll.

This compares with a final reading of 47.3 in August, the lowest since March 2009. A print above 50 indicates an expansion in activity while one below points to a contraction.

The closely-watched gauge of nationwide manufacturing activity focuses on smaller and medium-sized companies, filling a niche that isn't covered by the official data.

Wednesday's data weighed on investor sentiment in Asia, with stock indices in Sydney and Seoul widening losses to more than 1 percent each in the morning trading session. China stocks, however, trimmed losses to 0.9 percent, from an over 1-percent decline at the open.

A recent run of disappointing data has raised concerns around the health of China's economy, leading several banks and international institutions to pare growth forecasts for the country.

The Asian Development Bank on Tuesday cut its estimate for China's growth to 6.8 percent for 2015, down from its previous forecast of 7.2 percent and below 2014's 7.3 percent growth rate. It expects the growth rate of the world's second largest economy will fall to 6.7 percent in 2016.

Separately, Barclays also slashed its growth outlook on Tuesday for China to 6.6 percent and 6.0 percent for 2015 and 2016, from 6.8 and 6.6 previously.

The slowdown has also prompted market calls for bolder stimulus measures from Beijing and the country's central bank. Economists are hoping for greater clarity about the economy and policy in the context of President Xi Jinping's visit to the U.S.

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First Published:Sept 23, 2015 7:54 AM IST