SHANGHAI, China - Residents of a fishing village near Hong Kong said Friday that as many as 20 people had been killed by paramilitary police this week in an unusually violent clash that marked an escalation in the widespread social protests roiling the Chinese countryside. Villagers said as many as 50 other residents remained unaccounted for since the shootings on Tuesday.
   It is the largest known use of force by security personnel against ordinary citizens since the killings around Tiananmen Square in 1989. That death toll is still unknown, but is estimated to have been in the hundreds.
   The violence began after dark Tuesday in the town of Dongzhou, when the police opened fire on crowds to put down a demonstration over plans for a power plant. Terrified residents said their hamlet has been occupied since then by thousands of security officers, who have blocked off all access roads and were arresting residents who have tried to leave the area in the wake of the heavily armed assault.
   ''From about 7 p.m. the police started firing tear gas into the crowd, but this failed to scare people,'' said a resident who gave his name only as Li and claimed to have been at the scene, where, he said, a relative had been killed. ''Later, we heard more than 10 explosions, and thought they were just detonators, so nobody was scared. At about 8 p.m. they started using guns, shooting bullets into the ground, but not really targeting anybody. Finally, at about 10 p.m. they started killing people.''
   The use of live ammunition to put down a protest is almost unheard of in China, where the authorities have come to rely on the rapid deployment of huge security forces, tear gas, water cannons and other nonlethal measures. But Chinese authorities have become increasingly nervous in recent months over the proliferation of demonstrations across the countryside, particularly in heavily industrialized eastern provinces like Guangdong, Zhejiang and Jiangsu.
   By the government's own tally, there were 74,000 riots or other significant public disturbances in 2004 alone, a big jump from previous years.
   The Chinese government has not issued a statement about the events in Dongzhou, and the incidents have not been reported in the state news media. Reached by telephone, an official in the city of Shanwei, which has jurisdiction over the village, said, ''Yes, there was an incident, but we don't know the details.'' The official, who declined to give his name, said a government announcement would be made today.
   In phone interviews with more than a dozen villagers in Dongzhou, all of whom spoke on condition of anonymity for fear of retribution, a detailed account of the conflict emerged. Residents said their dispute with the authorities had begun with a power company's plans to build a coal-fired generator nearby, which they feared would cause heavy pollution. Farmers said they had not been compensated for the use of their land for the plant.
   Others said plans to fill in a local bay as part of the power plant project were unacceptable because people have made their livelihoods there as fishers for generations. Already, villagers complained, work crews have been blasting a nearby mountainside for rubble to use in the landfill.
   A small group of villagers was chosen to complain to the authorities about the plant in July, but the members were arrested, infuriating residents and leading others to join the protests. The police made more arrests Tuesday while villagers were mounting a sit-in, bringing many people out into the streets, where they obstructed several officers.
   In response, hundreds of law enforcement officers were rushed in. ''Everybody, young and old, went out to watch,'' said one man who claimed his cousin was shot dead in the forehead by the police during the protest. ''We didn't expect they were so evil. The farmers had no means to resist them.''
   The earliest accounts coming from the village said the police had opened fire only after villagers began throwing homemade bombs and other missiles. But villagers reached by telephone Friday denied those accounts, saying that a few farmers had launched ordinary fireworks at the police as part of their protest.
   ''Those were not bombs, they were fireworks, the kind that fly up into the sky,'' said one witness. ''At the moment the trouble started, many of the demonstrators were holding them, and of those who held fireworks, almost everyone was killed.''
   Villagers said that in addition to the regular security forces, the authorities had enlisted thugs from local organized crime groups to help put down the demonstration.
   Like the Dongzhou episode itself, most of the thousands of riots and public disturbances recorded in China this year have involved environmental, property rights and land-use issues. Among other problems with the growing rural unrest, the Chinese government is wrestling with a yawning gap in incomes between farmers and urban dwellers, as well as rampant corruption in local government.