BEIJING – As police battled to suppress deadly ethnic clashes last week in central China, tens of thousands of rice farmers fighting a dam project staged a huge protest in the western part of the country.

A week earlier, a large crowd of retirees demanding pension payments blocked traffic for days in a city in the east; nearly a thousand workers demonstrated outside a privatized department store in the northeast; and police used rubber bullets and tear gas to quell a mob of rioters in a western city.

The string of disturbances, described by journalists, witnesses and participants, highlights the daily challenge that civil unrest now poses to the ruling Communist Party. Despite economic growth that has lifted millions out of poverty, protests and riots in the world’s most populous country are occurring with increasing frequency, growing in size and ending more often in violence.

This expansion of social strife has yet to shake the party’s grip on power. But the trend, evident in the government’s own police statistics, has prompted alarm at the highest levels of the Chinese leadership, which has repeatedly declared social stability its top priority.

The Communist Party has indicated it is worried that these outbursts of discontent might coalesce into large-scale, organized opposition to its rule. The concern was apparent in a report by its Central Committee in September urging officials to improve governance and warning that “the life and death of the party” was at stake.

“The Soviet Union used to be the world’s number one socialist country, but overnight the country broke up and political power collapsed,” Vice President Zeng Qinghong wrote last month in the People’s Daily, the party’s flagship newspaper. “One important reason was that in their long time in power, their system of governing became rigid, their ability to govern declined, people were dissatisfied with what the officials accomplished, and the officials became seriously isolated from the masses.”

There were more than 58,000 major incidents of social unrest in the country last year, about 160 per day on average, according to the party magazine Outlook. That was an increase of 15 percent over 2002 and nearly seven times the figure reported by the government just a decade ago. Another study of police statistics, by Murray Scot Tanner, a scholar at the U.S.-based Rand Corp., concluded the demonstrations were growing in size while violence, including attacks on party and state officials, was also on the rise.

The party once blamed unrest on subversives and foreign agents, but it now acknowledges that many taking part in these protests have legitimate grievances. Officials also recognize that protests are inevitable in a rapidly changing country.

“Research institutes like our center are working on this issue day and night, and so is the government,” said He Zengke, executive director of the China Center for Comparative Politics and Economics in Beijing. “We all know the importance and urgency of the problem.”