Officials in a city in southwestern China where thousands of people clashed with police over a planned copper alloy project denied Tuesday that anyone died in the protest and warned against any further gatherings.

A government notice issued by the city of Shifang in Sichuan province told the public not to spread rumours and to safeguard social stability.

 A separate notice by the city's public security bureau warned the public not to use the internet or mobile phones to organize more protests and asked those who had done so to turn themselves in within three days or face severe punishment.

Thousands of people — including high school students — concerned about the pollution the plant would cause began to gather in front of the city government building and a public square Sunday night, and the protests turned bloody Monday afternoon after riot police moved in.

Public anger surged as internet users circulated photos and videos of riot police using tear gas and batons to end the protests. Some Internet users said one protester had died.

"People are very upset. How could the police beat them?" said a 15-year-old middle school student surnamed Liu, a local resident who did not protest.

Pollution causing unrest  

A man who answered the phone at Shifang No. 2 Hospital said that more than 30 people — including police officers and protesters — were injured but that they were discharged after minor medical treatment. The man, who declined to give his name, said no one had died.

The city government said it suspended the project after the protest and planned to educate residents about it.

Liu said parents, classmates and teachers all objected to the project because of its environmental risks.

"It will make our home city a town of death," Liu said.

Pollution problems are a leading cause of unrest in China as the country undergoes rapid economic development.

In recent years, Chinese have become more outspoken against environmentally risky projects in their backyards. Last year, authorities swiftly closed and moved an urban chemical factory from Dalian in northeastern China when 12,000 people protested.