The army said it was securing government offices and patrolling the capital's streets, after a night of unrest which included a military takeover of the state broadcaster.
The action triggered speculation of a coup, but the military's supporters praised it as a "bloodless correction".
Read our rolling coverage of Wednesday's events, as they happened, below:
"We wish to make it abundantly clear that this is not a military takeover," Zimbabwe Major General SB Moyo, Chief of Staff Logistics, said on television.
"We are only targeting criminals around [Mr Mugabe] who are committing crimes that are causing social and economic suffering in the country in order to bring them to justice.
"As soon as we have accomplished our mission, we expect that the situation will return to normalcy."
Neither Mr Mugabe nor his wife Grace, who has been vying to succeed her husband as president, have been seen or heard from.
At least three explosions were heard in the capital, Harare, overnight, and military vehicles were seen in the streets.
The army has been praised by the nation's war veterans for carrying out "a bloodless correction of gross abuse of power."
The military will return Zimbabwe to "genuine democracy" and make the country a "modern model nation," Chris Mutsvangwa, chairman of the war veterans' association, told the Associated Press.
The US Embassy closed to the public on Wednesday and encouraged citizens to shelter in place, citing "the ongoing political uncertainty through the night."
The British Embassy issued a similar warning, citing "reports of unusual military activity."
Good morning, welcome to The Independent's live blog on the latest updates from Zimbabwe.
The military says it has seized power of the capital and has President Robert Mugabe and his wife in custody.
It said it is securing government offices and patrolling the capital's streets following a night of unrest.
In the wake of the military takeover, the national police has recalled all officers from leave.
All police on leave have been ordered to return to their posts immediately, a police official told The Associated Press.
British nationals warned to stay indoors as military assumes control of ZimbabweBritish nationals in Zimbabwe's capital Harare are being advised to stay indoors amid reports of “unusual military activity”. The Foreign and Commonwealth Office (FCO) issued the guidance in the early hours of Wednesday morning following political tensions in the African country.
China said on Zimbabwe military chief General Constantino Chiwenga's visit to the country last week was a normal military visit.
China is closely watching the situation in Zimbabwe and hopes the relevant parties can properly handle their internal affairs, foreign ministry spokesman Geng Shuang told a daily news briefing.
Zimbabwe's army: This isn't a coupZimbabwe's army has said it has President Robert Mugabe and his wife in custody and is securing government offices and patrolling the capital's streets following a night of unrest that included a military takeover of the state broadcaster. The night's action triggered speculation of a coup, but the military's supporters praised it as a “bloodless correction”.
South Africa's President, Jacob Zuma, has urged the government of Zimbabwe and the Zimbabwe Defence Force to resolve the situation amicably.
Speaking on behalf of the Southern African Development Community (SADC), Mr Zuma expressed concern about the situation in Zimbabwe.
He called for calm and restraint, and expressed the hope that developments in Zimbabwe don't lead to unconstitutional changes of government, which would be contrary to the conditions of both the SADC and African Union.
The SADC will closely monitor the situation, he added, and remains ready to assist to resolve the political impasse in Zimbabwe.
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