BEIJING—Weekend protests forced officials in the eastern Chinese city of Ningbo to suspend a planned $8.9 billion petrochemical facility expansion, in the latest example of the rising power of an increasingly environmentally conscious public to delay or stop massive industrial projects.

Ningbo officials said late Sunday that plans to expand a refining and petrochemicals facility run by a unit of state-controlled oil-and-natural gas giant China Petrochemical Corp., known as Sinopec Group, would be suspended pending further review. In addition, the government said it would scrap a portion of the facility designed to produce the industrial chemical paraxylene, which local residents feared could be damaging to their health and the environment.

The protests are the latest case of heightened environmental awareness in China colliding with local government bids to shore up economic growth. In addition, they highlight apparent desperation by local officials to avoid social unrest at a period of particular political sensitivity in China.

A once-a-decade leadership change is set to begin Nov. 8, and security officials have called on local leaders in recent weeks to do everything possible to avoid disturbances ahead of the transition. The fear now for Beijing and local governments across China is potential for similar disturbances as part of China's burgeoning "not in my backyard" movement.

Protests against the facility appeared to intensify Saturday and Sunday. Photos posted online showed what appeared to be more than a thousand demonstrators outside the gates to the city's municipal government and elsewhere marching through the city's streets. Other photos showed police in riot gear scuffling with crowds of protesters, many of whom carried signs with slogans like "Save Zhenhai, Save Ningbo, Save China" and "we want to live, we want to survive." Zhenhai is the name of the city district where the petrochemicals facility is located.

Less than an hour after the government published its statement Sunday on Sina Corp.'s SINA -1.09% popular Twitter-like Weibo microblog service, the message had been reposted by users 56,000 times. Some users commenting on the statement demanded an apology from city officials.

Environmental protests are potentially less volatile than other forms of unrest in China, in part because residents' concerns are locally focused. Recent cases have shown that when local leaders are willing to make concessions, social order is quickly restored.

In July, protests in the western city of Shifang turned bloody after police used tear gas and stun grenades in an attempt to disperse crowds. As with the Ningbo protests, unrest in Shifang was for days among the most discussed topics on the Chinese-language Internet. Local leaders eventually agreed to cancel the planned $1.64 billion molybdenum-copper alloy plant.

Later that month, officials in the coastal community of Qidong in the eastern Chinese province of Jiangsu said they would stop construction of a pipeline intended to dump wastewater from a Japanese-owned paper mill into the sea, stopping a massive protest there.

For many watching the scenes of public empowerment in Ningbo from their computers at home, the protesters on Sunday emerged as victors. Photos trickled in as did a stream of raw commentaries, both celebrating the people's power and lamenting claims of violence by local officials. The claims couldn't be independently verified.

"I love and admire the people from Ningbo," wrote one Weibo user Sunday night. "Solidarity is strength."

It is unclear whether large numbers of protesters were detained during the demonstrations. An official at the city's foreign-affairs office said he didn't have any information on numbers of protesters arrested.

The Ningbo protests are the latest example of increasingly well-educated urban residents aggressively resisting the heavy industrial expansion that many local governments are encouraging to keep China's economy humming. In addition, it highlights how local government bids to lure lucrative investments to their cities are meeting increasing scrutiny from concerned residents.

The local government-run Ningbo Daily newspaper reported that the city's Communist Party chief, Wang Huizhong, and Mayor Liu Qi held meetings with representatives of the protesters on Saturday night. The report said the facility's expansion was "still in its early stages," and local officials would come up with a decision that reflected popular will. Ningbo is a relatively large coastal city with a population of around 7.6 million, located about 150 kilometers south of Shanghai.

Protesters in particular appear to be targeting the refinery's production of the industrial chemicals ethylene and paraxylene. Known as PX, paraxylene is an important chemical in the production of plastics and other goods. The demonstrations in Ningbo recall similar protests from August 2011 in the northeast city of Dalian, which also targeted a PX-producing facility. Local officials at the time promised to close the plant.

High levels of PX exposure can irritate the eyes and cause vomiting and respiratory discomfort, according to U.S. government and industry reports.

Sinopec didn't respond to a request for comment. The facility is already one of the country's largest, with a capacity of about 23 million tons of crude per year. An earlier Sinopec news release said the company would invest 55.9 billion yuan ($8.9 billion) in the plant's expansion.

Chinese and foreign companies have worked in recent years to ramp up production of petrochemicals, needed to produce everything from plastics and cleaning solvents and textiles. However, growing concern over potential health risks associated with these projects, as well as their proximity to population centers, threatens to further slow expansion efforts.

Sinopec Group controls New York-traded China Petroleum & Chemical Corp., SNP -2.00% also known as Sinopec Corp.