An investor watches an electronic board showing stock information at a brokerage office in Hangzhou city, Zhejiang province, Aug 21, 2015.[Photo/IC]

BEIJING -- China stocks tumbled on?August 21, following release of weak economic data.

The benchmark Shanghai Composite Index plunged 4.27 percent to close at 3,507.74 points, the sharpest weekly drop since the week ending July 3.

The Shenzhen Component Index dived 5.42 percent to close at 11,902.05. The ChiNext Index, tracking China's Nasdaq-style board of growth enterprises, slumped 6.65 percent to end at 2,341.95.

Companies in public transportation, communication, and highways suffered the most loss.

The shares plunged after the release of Caixin flash China general manufacturing PMI, which retreated to 47.1 in August from 47.8 in July, the lowest point since March 2009.

The flash index is published on a monthly basis ahead of final PMI data, making it the earliest available indicator of manufacturing sector operating conditions in China.

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