For six days last week, thousands of people protested in the streets in Jinshan, a Shanghai suburb.
They believe the government plans to build a chemical plant making paraxylene, or PX, a material used in polyester clothing and plastic bottles.
Jinshan's protests attracted thousands more people every day. They appeared to be tolerated by the authorities until they moved to heart of Shanghai, the city's financial centre.
Then, armed police swept in to shut down the demonstration. They arrested dozens of people on Saturday, hauling them away in three city buses.
"Those who yelled slogans were taken away," explained one person who participated in the protest. He would only give his surname, Zhang. "People were shouting things like 'Chemical refinery, stay out of Jinshan!'"
Mr Zhang told the BBC that some protesters are still in detention. However, it is unclear precisely how many people were arrested and how many remain under the watch of the police. Calls to the Jinshan and Pudong district police stations were not answered.
"We're protesting because there are already countless chemical plants in Jinshan, and we see more and more people have cancer here. We cannot tolerate more chemical plants," another protester, Mr Lu, told the BBC.
Large demonstrations against the construction of PX plants have occurred in other Chinese provinces, including Guangdong and Yunnan.
Increasingly well educated and affluent citizens are rejecting the construction of chemical plants near their homes. They have little faith that government safeguards will protect them.
Last Tuesday, after two days of protests, Jinshan's local government tried to appease protesters, arguing that plans for a new industrial park included an "advanced" PX refinery plant, not a production plant.
The government's implication is that a refinery would be less harmful to the surrounding environment than a production plant.
However, this is unlikely to placate citizens opposed to the plant.
"We don't care whether it is PX production or a refinery, but we know that they are chemical plants. Any chemical plant will have chemical waste, and we are really worried about the upcoming excessive waste," explained Mr Lu.