But Ningbo residents reached by phone said they were skeptical of the government’s sudden change of heart. “The announcement is just a way to ease tensions,” said Yu Xiaoming, a critic of the plant who took part in negotiations with the authorities on Sunday.

Image Credit... The New York Times

The protests, which began last week when farmers blocked a road near the refinery, grew over the weekend as thousands of students and middle-class residents converged on a downtown square carrying handmade banners and wearing surgical masks painted with skull and bones.

On Saturday, the demonstrations turned violent when riot police fired tear gas and began to beat and drag away protesters. At one point, according to people who were there, marchers tossed bricks and bottles at the police. At least 100 people were detained, according to some estimates, although most were later released.

The project, an $8.8 billion expansion of a refinery owned by the state-run behemoth Sinopec, was eagerly backed by the local government, which has been promoting a vast industrial zone outside Ningbo, a city of 3.4 million people in Zhejiang Province. Residents were particularly unnerved by one major component of the project: the production of paraxylene, a toxic petrochemical known as PX that is a crucial ingredient in the manufacture of polyester, paints and plastic bottles. Many residents contend that the concentration of polluting factories in the Ningbo Chemical Industrial Zone has led to a surge in cancer and other illnesses.

While mass demonstrations against mining operations, copper smelters and trash incinerators have disrupted Chinese cities in recent years, the construction of paraxylene plants has been especially controversial. In 2007, protesters in the coastal city of Xiamen, in Fujian Province, successfully forced the relocation of a PX plant that had been planned just 10 miles from downtown. Last August, officials in Dalian, in northeast China, announced that they would shut down a PX plant there after thousands of residents angrily confronted the riot police. That factory is still operating.