BEIJING (REUTERS) - Hundreds of people took to the streets of the Chinese city of Kunming on Thursday to protest against the planned production of a chemical at a refinery, the second demonstration this month against the project.

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

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

"To hell with the refinery, get PX out of Kunming," read the message on one of the banners, seen in a picture posted on Weibo.

Other pictures showed a heavy police presence, and at least some of the demonstrators appeared to have been detained by the police.

Calls to the Kunming Public Security Bureau and city government went unanswered.

There were no reports of violence.

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 fertilisers as well as PX, the company said in its submission to the NDRC.