In a sign the government's stance was toughening, state-run newspapers ran half-page articles warning 'subversive forces' were behind the mostly white-collar protests against plans to build a toxic chemical plant close to the city. Some 7,000 people marched last Friday and about 2,000 on Saturday.

'We will severely punish those taking part in illegal activities,' said police announcements in the Communist Party mouthpiece Xiamen Daily and the Xiamen Evening Post.

'The demonstrations have been organised by a small number of people who are inciting subversion ... do not mistake the government's restraint and patience for an admission of guilt, as that would be a major and extreme mistake,' a signed commentary in Xiamen Daily said.

'Nonsense,' said a 21-year-old marcher, surnamed San. 'We went out spontaneously.'

Tourists said they were inconvenienced by police roadblocks 1km around the city government's offices, an area that encompasses the Sofitel and the Marco Polo, two of Xiamen's most upscale hotels.

'We couldn't drive into the hotel at all,' a French visitor said. 'We had to get out and walk.'

Residents of the city say Tenglong Aromatic (Xiamen), which plans to annually produce 800,000 tonnes of the hazardous chemical p-Xylene, is too close to flats and schools. They believe it is an environmental and health disaster in the making. The city government says it is safe and the authority followed correct procedures in approving the project.

Foreign residents voiced sympathy with the demonstrators.

'I'd say don't build it,' said a foreign business owner, a resident for nine years. 'They want the money. And I have some sympathy for the government, they are running a country of 1.3 billion people, and 800 million of them are poor. But why do this here?'

The government believes Tenglong will add about 80 billion yuan to Xiamen's annual gross domestic product of 110 billion yuan.

Last week authorities said they were 'temporarily halting' the project pending a new environmental impact assessment. Demonstrators said they would wait and see.

In a further sign of intense pressure, residents received text messages from the government saying the plant's main critic - Xiamen University chemistry professor Zhao Yufen , a Chinese People's Political Consultative Conference (CPPCC) delegate - now supported it. In March, Professor Zhao organised an anti-plant petition signed by 105 CPPCC members.

The message, carrying what appeared to be Professor Zhao's signature, said: 'Zhao believes the government's position in re-evaluating the plant is a case of 'seeking truth from facts', and is proof the [authorities] fully respect the people's opinion and the environment.'