BELGRADE, Yugoslavia (AP) _ Baton-wielding police beat protesters Wednesday following a sweeping crackdown on Serbia's pro-democracy opposition and the seizure of the country's most popular independent media.

Hundreds of police in full riot gear charged into a rock-throwing crowd of opposition supporters at rally held late Wednesday to protest a police raid on Studio B Television, the country's largest media company not controlled by President Slobodan Milosevic's autocratic government.

Police also took control of three other independent media located in the same building _ B2-92 Radio, Index Radio and the privately owned daily newspaper Blic, infuriating pro-democracy activists. Another radio station in nearby Pancevo also was taken off the air Wednesday.

Opposition parties announced rallies would be held daily in some of Serbia's largest cities and were meeting late Wednesday on a strategy to keep up the protests.

``The regime has taken the country into a state of emergency,'' opposition parties said in a joint statement. ``Let us stand against this violence with all our energy because the future of our country is at stake.''

The move against the media followed the government's threat to clamp down on the opposition following the assassination Saturday of a regional official which authorities blame on Milosevic's critics.

Opposition leaders have denied any role in the killing and claimed the government was simply using the slaying as an excuse to snuff out the democracy movement and to silence dissenting voices ahead of elections later this year.

The government said Studio B was taken over because it had ``frequently called for the toppling of the constitutional order and rebellion against a legally elected government'' in Serbia, the main Yugoslav republic.

An estimated 30,000 people took to the streets within hours. Some first attended a late afternoon gathering outside Belgrade's City Hall, which owns Studio B, to listen to the station's journalists, who set up a makeshift, open-air program to read their evening news program over loudspeakers.

As another crowd of several thousand supporters _ mostly soccer fans _ tried to join the rally, riot police blocked the two groups from meeting up, causing a tense standoff that erupted into a clash.

At least five people were injured, including three demonstrators who were hospitalized with head injuries.

By Wednesday night, Belgrade's main shopping area was littered with debris, broken glass, overturned garbage cans, some smoldering after being set on fire.

Protests against the media closings were also reported in three other major Serb cities: 15,000 demonstrators turned out in Kragujevac in central Serbia and several hundred protested in Novi Sad, 44 miles northwest of the capital Belgrade, and in Mladenovac, south of Belgrade.

The pro-democracy student group Otpor, or Resistance, blamed for Saturday's slaying of a senior government official in Novi Sad, said at least 11 of its activists were detained by police Wednesday. Other members were arrested in previous days.

The nongovernment media are crucial for the opposition as they provide some balance in the otherwise biased reporting of the dominant state media staunchly supporting Milosevic.

An infuriated Aleksandar Cotric, head of Studio B's managing board, said, ``Milosevic's fascist-communist government that has for years been killing Serbian people has just killed Studio B.'' He added, ``We call on all Belgraders to come to defend their radio-television.''

Studio B continued transmitting Wednesday, but only as a relay for news programming from the government station. B2-92, predominantly a news station, broadcast only music on Wednesday.

A top opposition leader, Vojislav Kostunica, sent an open letter to Milosevic, warning of chaos and possible foreign intervention if the crackdown continues.

The Organization for Security and Cooperation in Europe condemned the crackdown and said it would urge Russia, Serbia's traditional ally, to use its influence to try to rectify the situation.