Zimbabwean Military has take control of the country but insists President Mugabe,a man who has ruled since 1880, is safe.
After seizing state TV, an army spokesman announced it was targeting people close to Mr Mugabe.
South Africa’s President Jacob Zuma said later that he had spoken to Mugabe and who said “was confined to his home but said that he was fine”.
The move may be a bid to replace Mr Mugabe with his sacked deputy, Emmerson Mnangagwa.
The dismissal of Mr Mnangagwa last week had left Mr Mugabe’s wife Grace as the president’s likely successor.
Heavy gun and artillery fire could be heard in northern parts of the capital Harare early on Wednesday.
A statement read out by a general on air denied it was a coup. There was no immediate word from the president himself.
Troops in armored vehicles have been out in the streets of the capital Harare since Tuesday.
After soldiers overran the headquarters of the ZBC broadcaster, Maj Gen Sibusiso Moyo went on air to say the military wished to “assure the nation that his Excellency the president… and his family are safe and sound and their security is guaranteed”.
Last month, Mrs Mugabe accused allies of Mr Mnangagwa of planning a coup.
The rivalry between Mrs Mugabe and Mr Mnangagwa split Zanu-PF.
Gen Chiwenga is a close ally of Mr Mnangagwa and both are veterans of the 1970s war which ended white minority rule.
The leader of the war veterans, Chris Mutsvangwa, welcomed the military move, telling Reuters: “This is a correction of a state that was careening off the cliff.
“It’s the end of a very painful and sad chapter in the history of a young nation, in which a dictator, as he became old, surrendered his court to a gang of thieves around his wife.”