BEIJING—A wave of violent unrest in urban areas of China over the past three weeks is testing the Communist Party's efforts to maintain control over an increasingly complex and fractious society, forcing it to repeatedly deploy its massive security forces to contain public anger over economic and political grievances.

The simultaneous challenge to social order in several cities from the industrial north to the export-oriented south represents a new threat for China's leaders in the politically sensitive run-up to a once-a-decade leadership change next year, even though for now the violence doesn't appear to be coordinated.

In the latest disturbance, armed police were struggling to restore order in a manufacturing town in southern China Monday after deploying tear gas and armored vehicles against hundreds of migrant workers who overturned police cars, smashed windows and torched government buildings there the night before.

The protests, which began Friday night in Zengcheng, in the southern province of Guangdong, followed serious rioting in another city in central China last week, plus bomb attacks on government facilities in two other cities in the past three weeks, and ethnic unrest in the northern region of Inner Mongolia last month.

Antigovernment protests have become increasingly common in China in recent years, according to the government's own figures, but they have been mainly confined to rural areas, often where farmers have been thrown off their land by property developers and local officials.

The latest unrest, by contrast, involves violent protests from individuals and large crowds in China's cities, where public anger is growing over issues including corruption and police abuses.

There is no evidence to suggest the recent violence is part of a coordinated movement—the party's greatest fear—nor do the events threaten its grip on power given the strength of China's security apparatus, and its booming economy, analysts say. They are nonetheless troubling for China's government which, unnerved by unrest in the Arab world, has detained dozens of dissidents since appeals for a "Jasmine Revolution" in China began circulating online in February. The Mideast uprisings so far haven't inspired similar mass protests in China.

The recent violence, however, has exposed the limits of the government's ability to control the urban population using a sophisticated array of tools from Internet censorship to surveillance—part of what party leaders refer to as "social management."

Authorities have turned to displays of raw power, deploying paramilitary police and armored vehicles in at least three cities in as many weeks, to prevent the violence from spiraling further as protesters have repeatedly directed their anger at government buildings, often ostentatious symbols of power.

What connects the violence is the way that a flashpoint—in the case of Inner Mongolia, the death of a Mongol at the hands of a Han Chinese truck driver, and in southern China, the assault by security personnel on a pregnant migrant worker—sets off much wider conflagrations.

The disturbances could reflect badly on President Hu Jintao, who has tried to promote the concept of a "harmonious society" and who is due to retire as party chief next year.

"There's an increasing sense of frustration that [leaders] are unable to put out a consistent, unifying message, even within the Party," said Kerry Brown, head of the Asia program at Chatham House, who met senior party officials last week. "Local officials are overreacting partly because of a lack of clear leadership at the top."

But the unrest is likely to strengthen the clout of Zhou Yongkang, who technically ranks ninth of nine on the Politburo Standing Committee but wields huge power as he oversees the police, intelligence agencies, prosecutors and courts.

Social unrest has been rising steadily in recent years: In 2007, China had more than 80,000 "mass incidents," up from above 60,000 in 2006, according to the Chinese Academy of Social Sciences, although many involved no more than a few dozen people protesting against local officials. No authoritative estimates have been released since then, though analysts citing leaked official figures put such incidents at 127,000 in 2008.

Since February, Messrs. Hu and Zhou have called for tighter restrictions on the Internet, which provides a conduit for people to share anger at government policies and malfeasance and learn about unrest.

Authorities have been careful to balance their use of force with conciliatory gestures, including the removal of some local officials. State media have also been reporting the unrest relatively quickly and openly, compared with previous years, in what some analysts see as an attempt by the government to take control of the narrative ahead of bloggers and other unofficial media.

A Monday editorial in the Global Times, a tabloid linked to the Communist Party, warned against trying to connect the recent incidents of unrest and draw conclusions about China's social stability. "China is not a nation where public anger collectively seeks to topple the existing order. It is time to debunk this ludicrous lie," it said.

The violence in Zengcheng, a town of about 800,000 near Guangzhou, began Friday night when security personnel pushed to the ground Wang Lianmei, a 20-year-old pregnant street vendor from the western province of Sichuan, as they tried to clear her stall from the road, according to state media. A crowd of migrant workers began attacking security guards and police with stones and bricks, as rumors spread that Ms. Wang had been injured and her husband, 28-year-old Tang Xuecai, killed, the state media reports said.

Local authorities tried to quell the unrest over the weekend by setting up a special task force to investigate the case, arresting 25 people and organizing a news conference at which Mr. Tang said that both his wife and their unborn child were unhurt, the reports said.

Xu Zhibiao, Zengcheng's Party chief, went to visit Ms. Wang in the hospital and took her a basket of fruit, the China Daily said.

But the violence flared again on Sunday night, witnesses said.

"We were all told not to go out on the street," said Dong Xingguo, a migrant from Sichuan who is working as an IT engineer in Zengcheng.

A Zengcheng government spokesman said: "Currently the situation in Zengcheng is stable. No death toll." He confirmed that there were still riot police on the streets to keep the peace.

Corrections & Amplifications

Chinese government offices were bombed May 26 in Fuzhou, Jiangxi Province. The map that accompanies this article incorrectly shows a city of the same name in Fujian Province.

—Andrew Browne

and Jason Dean in Beijing

and Yang Jie in Shanghai contributed to this article.

Write to Jeremy Page at jeremy.page@wsj.com