Chinese farmers have attacked a pharmaceutical plant and forced it to close, angered that its chemical waste was ruining their village's crops, polluting its river and harming their health, officials and residents said.

The Jingxin Pharmaceutical Company in Xinchang county in the eastern province of Zhejiang has been closed since July 4 when a group of villagers stormed it, a company statement said.

It did not say how many were involved in the siege, but a posting on a stock exchange online message board said 20,000 farmers rioted on Sunday after Jingxin said it would resume production.