Armoured units of the Thai military blocked the area around Prime Minister Thaksin Shinawatra's offices with tanks, witnesses said today.
Rumours of a military coup swept the Thai capital after an army-owned television station suspended regular programming and played patriotic songs.
On a government-owned TV station, Thaksin - now abroad on a visit to New York - declared a state of emergency.
"The Prime Minister with the approval of the cabinet declares serious emergency law in Bangkok from now on" Thaksin Shinawatra said on Channel 9 from New York. He said he was ordering the transfer of the nation's army chief to work in the Prime Minister's office, effectively suspending him from his military duties.
Several hundred soldiers were deployed at keys points in the capital of Bangkok, including government installations and major intersections, witnesses said.
Army-owned TV channel 5 interrupted regular broadcasts with patriotic music and showed pictures of the king. At least some radio and television stations monitored in Bangkok suspended programming.
The cable television station of the Nation newspaper reported that tanks were parked at the Rachadamnoen Road and royal plaza close to the royal palace and government offices.
Local radio station Ruam Duay Chuay Kan interrupted its programming just as a reporter was about to give information from Government House, where Thaksin has his office.