The city government responded with the mix of reassurances and warnings that Chinese officials often use in the face of protests over pollution and environmental concerns. “Currently, the project is still at the stage of preliminary assessment and comparing potential sites, and nothing has been finally decided,” the city government said in a statement issued on Sunday.

But officials did not rule out that the site chosen might be somewhere near Lianyungang, and they warned against any more protests. “The relevant departments will use the law to strike hard against a tiny number of lawbreakers who concoct and spread rumors and disturb the social order,” the city government said.

On Monday, there were no signs of renewed demonstrations in the city. But the residents had made their point: Another possible building block of China’s nuclear power expansion had come under passionate public attack, defying the police warnings and government attempts to defuse alarm.

The Chinese government has said that it will accelerate building nuclear power and processing plants to wean the economy more quickly off coal. In March, the national legislature endorsed a five-year plan that promises to push forward with more nuclear power plants and a reprocessing plant for used fuel from China’s growing number of reactors. Japan also has plans to open a reprocessing plant.

But in Lianyungang and elsewhere, fears over the safety of nuclear power — magnified by the Fukushima calamity in Japan in 2011 — could frustrate those plans.