Myanmar's military has seized power after detaining de-facto leader Aung San Suu Kyi and other senior members of her governing party.
All authority has been given to the top army commander and a one-year state of emergency has been declared, a statement on military TV said.
The coup follows a landslide election win by Ms Suu Kyi's National League for Democracy (NLD).
She urged her supporters "not to accept this" and "protest against the coup".
In a letter written in preparation for her impending detention, she said the military's actions put the country back under dictatorship.
In the early hours of Monday the military said it was handing power to commander-in-chief Min Aung Hlaing because of "election fraud". Soldiers are on the streets of the capital, Nay Pyi Taw, and the main city, Yangon.
Myanmar, also known as Burma, was ruled by the armed forces until 2011, when democratic reforms spearheaded by Aung Sann Suu Kyi ended military rule.
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 the UK, Prime Minister Boris Johnson condemned the coup and Aung San Suu Kyi's "unlawful imprisonment".