Government authorities declared martial law in a rural section of central China's Henan province last week after four days of ethnic clashes there involving thousands of villagers left as many as a dozen people dead and many more injured, witnesses said Monday.

The fighting occurred between farmers of the country's ethnic Han majority and the Muslim Hui minority living in neighboring villages, and between members from both groups and thousands of military police sent in to restore order. The incidents appeared to be among the worst ethnic violence known to have taken place in China in recent years.

The unrest was the latest reminder of the varied tensions tearing at this vast nation as it undergoes a difficult transition from socialism to capitalism while maintaining the ruling Communist Party's rigid political system. Hundreds of police fired rubber bullets at peasants protesting land seizures in a nearby village this summer, and thousands angry about corruption participated in riots in the western city of Chongqing two weeks ago.

In another incident, police in western Sichuan province clashed with demonstrators at the site of a proposed dam Friday, beating one man to death and injuring several others, residents said. More than 50,000 villagers participated in the protests, disbanding over the weekend only after officials promised to suspend construction and discuss compensation for farmland to be flooded.

In Henan, an official at a local mosque, who spoke on condition of anonymity, said the ethnic violence began Wednesday after a traffic dispute involving Hui truck drivers and Han villagers in Weitan, a corn- and wheat-growing hamlet located about 400 miles southwest of Beijing outside Kaifeng, the ancient Song Dynasty capital of China.

The fighting soon spread to several nearby villages, where witnesses reached by phone described mobs looting, burning down homes and beating people in alternating raids by members of the two ethnic groups. As many as 10,000 anti-riot and military police began pouring into the area beginning Friday, but villagers clashed with them, too, swinging iron bars and throwing bricks and stones, witnesses said.

State-run media reported nothing about the unrest for their domestic audience, complying with a news blackout ordered by propaganda authorities to avoid further inflaming ethnic tensions, reporters said. But the world service of the official New China News Agency carried a brief report saying seven people were killed and 42 injured in "fighting" between Wednesday and Sunday. The report said 18 people had been arrested.

The clashes appeared to have been exacerbated by the arrival of hundreds of Muslim Hui from other parts of the country who rushed to the region to support their ethnic brethren. Military police set up checkpoints and, with the help of local imams, persuaded many of the outsiders to go home, the official at the mosque said. But residents said some eluded police and joined the clashes.

China formally recognizes 56 ethnic groups, with the Han making up over 90 percent of the country's population of 1.3 billion. Numbering about 10 million, the Hui are one of the largest minorities and consider themselves descendants of Han who converted to Islam and of intermarriages between Han and Arabs who migrated to China centuries ago.

Hui warlords were among the last rulers to put up strong resistance to the Communists before Mao Zedong took power in 1949. The government remains nervous about relations with the Hui, and outbreaks of unrest sometimes erupt after minor provocations.

The initial clash in Henan involved seven Hui truck drivers and a small group of Han villagers blocking a road, the mosque official said. He said other Han came to the defense of the villagers, beat the drivers and set fire to their trucks. The next day, the villagers stopped two buses, forced the mostly Hui passengers to disembark and set fire to the buses, he said.

Rumors spread quickly, and Han and Hui soon began launching attacks on each other's communities, residents said. Provincial officials arrived Friday with more than 2,000 military police but were unable to contain the clashes until Sunday, after thousands of reinforcements arrived.

One local journalist, who spoke on condition of anonymity, said a government source told him nearly 150 people were killed in the rampages, including several police officers, but he was unwilling to provide details and local officials denied the account. Several residents, including village doctors who treated the wounded, said they knew of only about a dozen fatalities.

The party chief of one of the Hui villages involved in the violence, who gave only his surname, Ma, said about 10 people died in the clashes. "Under the concern of upper-level officials, people in our village are calm now," he added.

But both Hui and Han residents said the atmosphere remained tense. Residents reported being ordered to cook round the clock to feed the large numbers of troops deployed to the region.

Du Pingfang, 40, a Hui doctor in Nanren village, said his neighbors remained frightened because the Han had threatened kill all Hui over the age of 3. "More than 5,000 soldiers have surrounded our village to protect us, but we're still worried that the Han will launch a surprise attack," he said.

Han residents also expressed fear, alleging that Hui were continuing to arrive in the region from across China. "Many police have been sent here to control the situation," said an elderly schoolteacher in Xilang village who fled and hid in the fields during much of the violence, "but they can't stop the Hui from coming."

Chinese police stand guard in Henan province, where Han villagers clashed with Muslims from the Hui minority.