Myanmar's military has taken control of the country after Aung San Suu Kyi and other political leaders were arrested in the early hours.
Hours after the arrests, military TV confirmed a state of emergency had been declared for one year.
The coup comes after tensions rose between the civilian government and the military following a disputed election.
Myanmar, also known as Burma, was ruled by the military until democratic reforms began in 2011.
The military said on Monday it was handing power to commander-in-chief Min Aung Hlaing. Soldiers are on the streets of the capital, Nay Pyi Taw, and the main city, Yangon.
In November's election, Ms Suu Kyi's National League for Democracy (NLD) won enough seats to form a government. The army says the vote was fraudulent.
The coup appears to be a clear violation of the constitution drafted by the military more than a decade ago, and which it promised to honour only on Saturday. Detaining political leaders like Ms Suu Kyi is a provocative and very risky move, one which may well be strongly opposed.
What has the reaction been?
The United States has condemned the coup, saying Washington "opposes any attempt to alter the outcome of recent elections or impede Myanmar's democratic transition".
US Secretary of State Antony Blinken called for the release of all government officials and civil society leaders and said the US "stands with the people of Burma in their aspirations for democracy, freedom, peace, and development. The military must reverse these actions immediately."
In Australia, Foreign Affairs Minister Marise Payne said "we call on the military to respect the rule of law, to resolve disputes through lawful mechanisms and to release immediately all civilian leaders and others who have been detained unlawfully."
John Sifton of Human Rights Watch said: "The military junta that ruled Myanmar for decades never really stepped away from power in the first place."
"They never really submitted to civilian authority in the first place, so today's events in some sense are merely revealing a political reality that already existed."
"The doors just opened to a very different future," Thant Myint-U, Yangon-based historian and author described the outlook. "I have a sinking feeling that no one will really be able to control what comes next."
"And remember Myanmar's a country awash in weapons, with deep divisions across ethnic and religious lines, where millions can barely feed themselves."
Situation on the ground?
Mobile internet data connections and some phone services have been disrupted in major cities, while the state broadcaster MRTV says it is having technical issues and is off air.
Communications with Nay Pyi Taw are down and it is difficult to assess the situation there.
In the country's largest city and former capital Yangon, phone lines and internet appears to be limited, with many providers cutting their services.
There are reports that people in Yangon are rushing to get money from ATMs amid expectations of a cash crunch in the coming days.
Some ATMs already appear to not be working and it's unclear whether banks will open.