The city in the wealthy eastern province of Fujian announced on Wednesday it was suspending construction of a plant to make paraxylene (PX), a petrochemical that goes into polyester and fabrics.

Angry locals had denounced the project as an "atomic bomb" threatening the seaside environment, and they claimed to have circulated nearly a million mobile phone text messages urging families and friends to protest against the plant.

"On my way to work today, I saw a lot of people marching on the main streets, holding banners and some wearing gas masks," a computer engineer surnamed Huang told Reuters.

"One of the banners said 'don't suspend, cancel the plant'," he said. "If the project goes ahead, it will damage the environment and a lot of people's health as it is close to the city centre."

Protesters marched to the city government offices on Friday morning and demanded the resignation of the Communist Party Secretary of Xiamen, He Lifeng, the first witness said, adding that the demonstrations, initiated by students at Xiamen University, were peaceful.

China's leaders have promised to clean up skies and water degraded by decades of unchecked growth, and environmental agencies are increasingly vocal about officials who push industrial projects without assessing the impact.

But many local governments remain eager to boost employment and revenues even if the environment suffers.

The size of the demonstration in a country whose Communist rulers are keen to maintain social stability and frown on public protest also attests to the power of mobile phones and the Internet to rally the public.

Huang said he and some friends and neighbours had all received text messages urging citizens to join the protest.

Debate over the plant began to grow during the annual session of China's parliament in March, before public opposition built up through the Internet.