The violence ended quickly as most of the security forces withdrew and the red-shirted protesters took over the station’s compound. The antigovernment station had been taken off the air as the government’s main action in enforcing a state of emergency declared Wednesday.

Soon afterward, officials announced that the station, the People’s Television Station, would resume broadcasting, a significant victory for the protesters in challenging the writ of the government of Prime Minister Abhisit Vejjajiva.

The scenes at the station seemed to suggest the prevailing winds of the moment, as soldiers with their helmets and riot shields departed single file between rows of cheering protesters, exchanging smiles and slaps on the back. One soldier, with a red ribbon tied around his wrist, raised a fist.

Several casualties were reported on both sides, but witnesses said the security forces did not appear to have made a determined stand in the face of a vigorous charge by mostly unarmed protesters.

One witness said some soldiers had fled their own tear gas as it blew back into their faces.

The protesters, who are mostly supporters of the fugitive former prime minister, Thaksin Shinawatra, are demanding that the government step aside and call a new election. Mr. Abhisit took office in a parliamentary vote in December 2008, when a previous pro-Thaksin government was dissolved by a court for electoral fraud.

Analysts say that the military was involved behind the scenes in installing Mr. Abhisit’s government. As the challenge by the protesters, known as the Red Shirts, has escalated, the allegiance of the military has become a subject of discussion among political analysts. The protesters mostly represent the country’s poorer classes in a long-running challenge to the country’s traditional ruling elite, which includes high-ranking military members.

Until Friday, both the government and the protesters had been at pains to avoid violence, which both feared could escalate into chaos and could discredit their causes.

Under the emergency decree, the government had shut down the Red Shirts’ television channel as well as Internet sites sympathetic to the protesters and to Mr. Thaksin, who was ousted in a coup in 2006 and is now abroad, evading a jail term on a corruption conviction.

Arrest warrants have been issued, but apparently not enforced, for several protest leaders. The government has so far taken no other action to enforce the decree, which allows the military to disperse crowds in the streets and to arrest their leaders.

Mr. Abhisit has been the subject of increasing criticism, and even derision, for failing to take stronger steps to clear away the protesters, who have paralyzed the commercial heart of Bangkok, forcing the closing since Saturday of several malls, hotels and banks.

On Wednesday, a group of protesters humiliated the government by storming the Parliament building and forcing cabinet ministers to flee over a back wall for evacuation by helicopter.

Hours later, Mr. Abhisit announced the emergency decree and set up a joint civilian-military crisis center empowered to impose curfews, ban public gatherings and censor the news media.

On Thursday night, Mr. Abhisit addressed the nation on television, repeating a pledge not to use strong-arm measures to quell the demonstrations and explaining his decision to bar antigovernment information.

“What the government wants is peace and happiness,” he said. “It is the manipulation of information that is creating hate.”

Most television stations are owned by the government. But a number of national and local television and radio stations are in private hands, and many outlets, particularly in the rural heartland, are virulently antigovernment.

Protesters who have gathered among the glass-fronted high rises in the commercial district live in a constant din of speeches and broadcasts that pound home the views of their leaders.

“I am here to ask for democracy,” said one protester, Tassanee Rattanapunsak, 46, who sells car parts and wore a headband announcing her love for Mr. Thaksin. “If I stay at home, I don’t know anything. The government closes my eyes.”

Mr. Thaksin, who has become a tech-savvy fugitive, has been communicating with his supporters through video links and radio broadcasts. Most recently, his medium of choice has been Twitter.

“The worst thing is to have a dictatorial government that blocks the media and forces media organizations that are not neutral to be used as political tools,” he said in a Twitter message on Friday afternoon.

On a more personal note, the former prime minister, who has based himself mostly in Dubai after being told that he was unwelcome in Britain and elsewhere, wrote in a Twitter message: “Tomorrow I will travel to Saudi Arabia at the prince’s invitation. The prince has invited me to join him in constructing a new city near Mecca.”