It was their second such protest against yeast producer AB Mauri Vietnam in Dinh Quan District.

Local authorities said the company had broken its promise last year to comply with environmental regulations.

In July 2009 the people had agitated after the company released wastewater into the Tri An reservoir and caused such severe pollution that the provincial authorities closed it down for three months.

The company had then promised to cease operations if it continued to cause pollution.

Locals said it had continued to discharge wastewater without proper treatment into the river, affecting their fishing activities.

It also released fumes, they said.

Water samples taken from many wells in the area had all failed to meet the country’s safety standards, the provincial Preventive Health Center reported.

Two of them even contained arsenic, a carcinogen, it said.

Water from the La Nga River near the company had a much higher content of iron than allowed, it added.

Provincial agencies and the anti-environmental crime police have fined the company hundreds of millions of dongs on four occasions for its violations.