Anti-government protesters have welcomed the announcement of martial law, but academics and human rights groups blasted it for putting the future of the country in the hands of the army chief.
Sunai Phasuk, Thailand's Human Rights Watch representative, said there was not enough justification for army chief Prayuth Chan-ocha resorting to a 100-year-old law. Invoking the law was a serious blow to the country's already fragile democracy, he said.
“There have been no fatal confrontations and martial law has been declared nationwide to ensure the army can take over the elected civilian government completely,” said Mr Sunai.
“The media cannot function properly and checks and balance mechanisms are now in the hands of a single person. This is a scary prospect for Thailand.”
However, Kasian Tejapira, a Thammasat University political science professor, said the outcome would not only depend on Gen Prayuth but also on how acting caretaker Prime Minister Niwattumrong Boonsongpaisan reacts to developments.
He said martial law was a safety net for the People’s Democratic Reform Committee (PDRC) to step down from its "political suicide mission" and also to stop the United Front for Democracy against Dictatorship (UDD) from moving beyond their Bangkok protest site on Utthayan Road.
Mr Kasian said army intervention would force all parties to find a way out of the crisis under the shadow of the military.
He was concerned Mr Niwattumrong may abandon his link to democracy.
“Like it or not, a scheduled election, most likely overseen by the military, will be part of the deal.
"There will be a push to change the acting PM to someone more congenial to the opposition,” said the political scientist.
"The issue is whether the deal would be done under the constitution, as an acting prime minister of a caretaker government whose main job is to prepare for a general election, or by the suspension of some provisions of the constitution, to have a temporary government with full authority to institute so-called reform,'' he said.
The latter, he said, would amount to an interim unelected government in violation of the current constitution and democratic principles upheld by the public.
“I'm afraid the military prefer the latter option and the caretaker government is likely to yield to it,” said Mr Kasian.
Meanwhile, anti-government protest leader Suthep Thaugsuban initially said he accepted the military's order for his protesters to stay put at their protest sites.
He cancelled PDRC marches yesterday, but activities at the PDRC's Makkhawan bridge stage are still going ahead.
Gen Ekkachai Srivilas, director of the Office of Peace and Governance at King Prajadhipok's Institute, said that in his opinion the declaration of martial law would result in more positive consequences than negative ones.
Rallies are still allowed under martial law, but they must be contained within their present sites, said Gen Ekkachai.
However, verbal attacks must be avoided, those who defy the law may be sued and the cases against them will go to a military court, he warned.
Any broadcast or publication that could incite unrest is also banned.
Police must report directly to the new Peace and Order Maintaining Command (POMC), but the caretaker government will still perform its duties, said Gen Ekkachai.
One negative outcome is the invocation of martial law will erode the credibility of the country in the eyes of the international community, he said.
Government agencies will be asked to report to the POMC.