Even before the Wuhan protests began, residents had been complaining online about the smell from a large landfill at the site of the proposed incinerator. The local government tried to reassure them by announcing that it was putting thicker plastic film over the waste and installing an air purification system.

Street protests were set off by noisy construction work near the landfill that apparently led some residents to believe that work on the incinerator had begun. But the Xinzhou district government said the noise was from the demolition of a nearby rail line.

It said that while planning had been underway for an incinerator in the area, it would not proceed until environmental impact assessments had been carried out, and that the public’s views on the project would be taken into account. That did not mollify protesters, who feared that the consultation process would still end in construction of the incinerator.

Periodic protests against incinerators have been breaking out for a decade in China. But the ones in Wuhan appear to have been larger than most, although a protest against an incinerator in Hangzhou in 2014 was more violent, with at least 10 demonstrators and 29 police officers injured.

Older incinerators in China have been a source of emissions that can damage the body’s nervous system. Such pollutants, particularly long-lasting substances like dioxin and mercury, are not only dangerous in China but can also float on air currents across the Pacific, reaching as far as the United States, according to atmospheric research based on satellite observations.

Better incinerator technology that eliminates almost all emissions, already used widely in Europe, is now available in China, but it is many times more expensive to install. Chinese officials have tried hard to persuade the public that new incinerators are being built with such improved technology.