About 2,500 people have taken to the streets to protest against plans for a new oil refinery on the outskirts of the southern Chinese city of Kunming.
Government officials said earlier in the week that the project, being built by the powerful state company PetroChina, would meet environmental standards and was crucial to the local economy.
However, local people remain worried that the refinery, which is expected to produce up to 10 million tonnes of refined oil annually, will pollute the air and water.
Demonstrators also want the government to make the project's environmental evaluations public.
Protests, lawsuits and discussion in China's active social media about environmental concerns have become more frequent in recent years.
In particular, fuel processing and refining have been the cause of huge demonstrations by the middle class in affluent cities such as Dalian, Ningbo or Chengdu, in some cases prompting officials to scrap or delay the plans.
At least two people were briefly detained at Thursday's protest but later released, according to relatives and friends interviewed by the AP news agency.
The detentions came as protesters made their way to the commercial centre of Kunming, near the headquarters of the provincial government.
Later, scuffles with the police led to protesters making their way onto side streets and to march along the city's People's Avenue, while shouting slogans against the city's mayor, Li Wenrong.
He Bo, a deputy with the city government, appeared at the scene and tried to reach out to protesters, inviting them for a discussion with the government.
But the official, who was followed by state media cameras, failed to find representatives of the demonstrators who were willing to talk.
He finally gave up and abandoned the scene, escorted by security agents.
Lack of transparency
The protests underline the failure of the government to reach out to the public, as well as their inability to make the process of decision-making more transparent.
The protests also highlight the lack of measures to strengthen environmental protection as promised by the central government.
Local and provincial governments still see more incentives in projects that aim to boost gross domestic product growth at, what could be argued, the expense of environmental concerns.
"I think we, the people of Yunnan, already have a pretty good life. We don't need speedy development. What we need is a healthy and peaceful country," said one local resident, Liu Yuncheng.
Earlier in the week, the deputy director of the Yunnan provincial Development and Reform Commission defended the project on environmental and economic grounds, but said that the Environmental Impact Assessment report for the refinery project remained a classified document.
The remarks by Ma Xiaojia have fuelled discontent, some of the protesters said on Thursday.
Authorities have been trying to build up an oil supply chain to Yunnan as the province currently imports all its oil from other areas of the country.
A key part of the plan is the Myanmar-China pipeline, which after eight years of planning and construction is due to start pumping oil and gas at the end of the month.
China has invested heavily in the project to access resources from the neighbouring country and establishing a new, shorter route for oil and gas procurement, as an alternative to the Malacca strait.
Opposition to the pipeline has been strong on both sides of the border and recently officials from Myanmar said there would be delays to the start of the operation.
The refinery plant in Anning, 35km from the Kunming city centre, would be a key project to process the fuel coming through Myanmar, and its completion by 2014 should meet 54 percent of the 14 million tonnes of oil needed in the city according to officials.