The announcement came just hours after street fights broke out between thousands of supporters and opponents of embattled Prime Minister Samak Sundaravej, who has resisted mounting pressure to step down.

One person was killed and dozens injured in the violence near the main government complex occupied for a week by activists who want Samak to resign, claiming he is merely a puppet for ousted premier Thaksin Shinawatra.

"Because last night there was unrest affecting the peaceful law and order in the country and obstructing the democratic process, the government has declared a state of emergency, which will affect people's individual freedoms," said the announcement read on state radio.

Samak appointed the powerful army commander General Anupong Paojinda to head a special team tasked with enforcing the emergency decree, with the national police chief and Bangkok's regional army commander as his deputies.

The announcement said Anupong now had the power to break up any gathering and to force people to leave any location.

"By invoking this emergency decree, Anupong can ban people from entering any specific place and can evacuate people from any specific place," it said.

Thai police called in army reinforcements early Tuesday morning to rein in the protests, setting nerves on edge in a country that has seen 18 military coups since the end of absolute monarchy in 1932.