Thailand's army chief seized power in a military coup on Thursday, ordering rival protesters off the streets and deposing the government in a bid to end months of political bloodshed.

General Prayut Chan-O-Cha made the announcement in a televised address to the nation, saying the powerful armed forces had to act to restore stability in the Southeast Asian nation.

The military declared a nationwide curfew from 10pm to 5am and ordered demonstrators on both sides of the kingdom's political divide to disperse and go home after nearly seven months of political rallies in the capital.

It banned gatherings of more than five people, summoned the ousted cabinet to report to the army and suspended the constitution – except for the section related to the monarchy.

Moments before Prayut's stunning announcement, witnesses said they saw leaders of Thailand's two main political parties and its rival protest movements being taken by the military from a venue where Prayut had convened talks aimed at resolving their differences.

It was unclear if they had been formally detained.

The tough-talking Prayut, 60, said he seized power because of "the violence in Bangkok and many parts of the country that resulted in loss of innocent lives and property and was likely to escalate."

It is the latest twist in a nearly decade-long political crisis stretching back to an earlier coup in 2006 that deposed the controversial tycoon-turned-politician Thaksin Shinawatra as premier – a move that infuriated his supporters.

'Remain calm'

"All Thais must remain calm and government officials must work as normal," Prayut said in the brief announcement around 5pm (1000 GMT), flanked by four of his top officers.

Rumours of an imminent coup had gripped Thailand since Tuesday, when the army chief declared martial law to prevent deadly political tensions spiralling out of control.

The overthrow caps months of increasing political tension pitting a Bangkok-based royalist elite and its backers against the democratically elected government aligned to Thaksin, whose sister Yingluck was dismissed as premier earlier this month in a controversial court ruling.

Thaksin now lives in Dubai to avoid prison for a corruption conviction, but he and his political allies retain strong support in Thailand, particularly in the rural north, and have won every general election since 2001.

Prayut's announcement came shortly after the opposing camps and other top political actors had gathered for a second straight day of closed-door reconciliation talks at a heavily guarded military facility in the capital Bangkok.

Some experts expressed fears the military takeover could unleash more turmoil.

"The coup is not a solution at all to end the crisis. This will become the crisis," said Pavin Chachavalpongpun of the Centre for Southeast Asian Studies at Japan's Kyoto University.

"It shows the military has never learned the lesson from 2006," he said, referring to the cycle of political crisis stemming from Thaksin's overthrow.

Pavin said the coup would make anti-government protesters "very happy".

Protests by the anti-Thaksin movement have rocked Thailand for months. Related violence has left at least 28 people dead and hundreds wounded.

The army chief likely took over due to the weakened caretaker government's refusal to make way for an interim regime, said Paul Chambers of the Institute of Southeast Asian Affairs at Chiang Mai University.

"Since the caretaker government was resisting moving to an ad hoc prime minister, Prayut was pressured to take the 2006 option," he said.

Caretaker premier Niwattumrong Boonsongpaisan, who had refused calls to step down, was among the ministers ordered to report to the army.

Niwattumrong was "safe" in an undisclosed location, an aide said.

Prayut, a staunch royalist aligned with the anti-Thaksin bloc, had earlier vowed not to allow Thailand to become another "Ukraine or Egypt."

"What I am doing in my security capacity – if I upset anyone, I apologise but it is necessary," he said on Thursday before the coup announcement.

Thailand's democratic development has now been repeatedly been curbed by a total of 19 actual or attempted coups since 1932.

Martial law gives the military wide powers to ban public gatherings, restrict movements, and detain people, though most of those powers had not been invoked before the coup.

The military has taken steps to muzzle the media since Tuesday. On Thursday it announced after the coup that all public and private television and radio stations must suspend normal programming and only broadcast army feeds.

Prayut gave no indication how long the military would hold power. He said it took over in order to "start political reform", without giving details.

The pro-Thaksin "Red Shirt" movement had called for new national polls they hope will provide a fresh mandate to the beleaguered elected government.

But the anti-government movement has first demanded vague political reforms that are widely seen as a bid to cripple the political power of Thaksin's family and allies, and some Thais welcomed the army takeover.

Arnusit Chenruk, a 39-year-old Bangkok office worker, said the coup was a "good" thing.

"Our country has been chaotic and has had no solutions for a long time."