Hundreds of people took to the streets of the Chinese city of Kunming on Saturday to protest against the planned production of a chemical at a refinery, in the latest show of concern over the effects of rapid growth on the environment.

China's increasingly affluent urban population has begun to object to the model of growth at all costs that has fuelled the economy for three decades, with the environment emerging as a focus of protests.

Photographs on Weibo, China's version of Twitter, showed a crowd of protesters in the centre of the southwestern city, carrying banners protesting against production at the planned plant of paraxylene (PX), a chemical used in making fabrics and plastic bottles.

Some estimated the crowd was up to 2,000-strong but the official Xinhua news agency said in a report more than 200 people had gathered to protest, many wearing masks printed with slogans including "no PX in Kunming".

They attracted nearly 1,000 onlookers, Xinhua said.

"Give me back a beautiful Kunming. We want to survive, we want health, get PX out of Kunming", read one of the banners, seen in a photo posted on Weibo.

A man at the Kunming Public Security Bureau, who described himself as a member of staff on duty, said he was not aware of the incident. The city government's emergency department referred a phone call to another number, which was not answered.

There were no reports of any violence at the protest.

Last November, the eastern city of Ningbo suspended a petrochemical project after days of street protests. The year before, big protests against a PX plant in the northeastern city of Dalian forced the city government to suspend it.

More recently, heavy pollution that has blanketed the capital Beijing and other cities, as well as scandals over food, have added to the sense of unease.

China National Petroleum Corp, the country's largest oil and gas producer and supplier, announced in February that the National Development and Reform Commission (NDRC) had approved the refinery project at Anning, just outside Kunming.

The refinery would produce gasoline, diesel, other various chemicals and fertilizers as well as PX, the company said in its submission to the NDRC