BEIJING, Feb. 1-- Chinese shares began the month on a weak note, as a key indicator of manufacturing activity fell to its lowest level since August 2012.

The benchmark Shanghai Composite Index declined 1.78 percent to close at 2,688.85 points while the smaller Shenzhen index lost 1.02 percent to close at 9,322.01 points.

The ChiNext Index, which tracks China's NASDAQ-style board of growth enterprises, was down 0.07 percent to close at 1,992.7 points.

Total turnover on the two bourses waned, standing at 370.4 billion yuan (56.52 billion U.S. dollars).

Financial heavyweights led the decline, with the largest, CITIC Securities, down 1.86 percent to close at 14.23 yuan.

Sub-indexes related to oil, coal and steel were among the worst performers on Monday.

Oil giant PetroChina plunged 2.82 percent and closed at 7.25 yuan.

After exhibiting the worst monthly performance since October 2008 in January, Chinese shares dipped below the 2,700-point mark again on Monday despite fleeting comfort brought by the surge on Friday.

Market sentiment was depressed on the release of new purchasing managers' index (PMI) data. The index came in at 49.4, down from December's 49.7, according to the National Bureau of Statistics and the China Federation of Logistics and Purchasing.

The PMI signalled persistent weakness in manufacturing activity.

NBS statistician Zhao Qinghe attributed the retreat to slowing factory activity ahead of the Chinese New Year holidays in early February, as well as China's ongoing campaign to resolve excess capacity.