What is happening on the ground?
The cabinet has been ordered to report to the military and gatherings of more than five people have been banned.
A nationwide curfew is in force between 22:00 and 05:00 local time. The broadcast media have been told to suspend all normal programming.
A military statement said army chief Gen Prayuth would head a ruling military body - the National Peace and Order Maintaining Council - but that the upper house of parliament and courts would continue to function.
Political party leaders, including opposition leader Suthep Thaugsuban, were taken away from a venue where they had been holding talks with the army after troops sealed off the area.
Shortly after the coup announcement soldiers moved rapidly on the "red shirt" camp on the outskirts of Bangkok, as well as towards the anti-government demonstrators' camp in the centre of town. Troops fired into the air to disperse the pro-government protest camp but there are no reports of major violence.