Zimbabwe is now under military control, with soldiers patrolling the streets of Harare and the army in control of state TV.
President Robert Mugabe is said to be confined to his home.
However, army spokesman Major General Sibusiso B Moyo insists it is not a coup.
"We wish to make it abundantly clear that this is not a military takeover of government."
He says the action is an intervention to stop criminal activity in the country.
It's understood the President's wife, Grace Mugabe, has fled to Namibia. She is next in line for the presidency after Mr Mugabe sacked his deputy, which is what is thought to have sparked the military action.
Coup? What coup?
In the annals of missed stories, it ranks up there.
When Wednesday's edition of The Herald, Zimbabwe's main state newspaper, hit the streets, Zimbabweans were surprised to learn that talk of ructions between President Robert Mugabe's ruling ZANU-PF party and military chief Constantino Chiwenga were unfounded.
"ZANU-PF unfazed by Chiwenga," the Herald declared on its front page, reporting on the party's denunciation of the military chief as a traitor the previous day.
Most people in Harare had spent the night glued to social media and the internet for updates on a coup slowly unfolding against 93-year-old Mugabe, Zimbabwe's leader of the last 37 years.
Just after 4am, an army spokesman in camouflage fatigues appeared on state media to announce that the army had seized power. The final line of his declaration: "To the media, we urge you report fairly and responsibly".
Call for calm
The European Union has called for dialogue in Zimbabwe and a peaceful resolution to the crisis that erupted there overnight as the military seized power.
"The recent political developments in Zimbabwe, and their spillover, including in relation to the country's security forces, are a matter of concern," said a spokesman for the European Commission, the EU executive.
"We are following the situation closely and we want to underline that the fundamental rights of all citizens need to be respected and the constitutional order and democratic governance needs to be upheld," he added in a statement.
"We call on all relevant players to move from confrontation to dialogue with the aim to a peaceful crisis resolution."
Reuters / Newshub.