There have been reports of a heavy military presence and explosions in Harere.
The Zimbabwean military took control of the country on Wednesday in what it described as a quest to drive out "criminals" close to 93-year-old president Robert Mugabe.
Uniformed soldiers took over Zimbabwe's state broadcaster, ZBC, and broadcast a statement to the nation in which a senior officer from the Zimbabwe Defence Forces denied that the military was staging a coup.
Soldiers could be seen deployed on the streets of the capital, Harare, alongside armoured assault vehicles.
The military said that Mugabe and his family are "safe and sound." The president of neighbouring South Africa, Jacob Zuma, said in a statement that he had spoken to Mugabe and that he was unharmed but confined to his home.
The military overthrow was accompanied by reports of explosions and gunfire in the capital city Harare.
As daylight broke, a witness told Reuters that soldiers and armored vehicles were cutting off road access to government offices, parliament, and courts in central Harare.
The news agency also reported that the country's finance minister had been detained by the military.
In their statement on Wednesday, the military said their aim was to "pacify a degenerating political, social and economic situation" in Zimbabwe, then to give back power.
Major General S.B. Moyo, the army's Chief of Staff Logistics, said:
"We wish to assure the nation that his excellency the President of the Republic of Zimbabwe and commander-in-chief of Zimbabwe defence forces comrade R.G. Mugabe and his family are safe and sound and their security is guaranteed.
"We are only targeting criminals around him 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."
He also called on veterans and security forces to cooperate, saying that "any provocation will be met with an appropriate response."
"To both our people and the world beyond our borders, we wish to make it abundantly clear that this is not a military takeover of government.
"What this mobile defence force is doing is to pacify a degenerating political, social and economic situation in our country which if not addressed, may result in a violent conflict."
The military action comes shortly after a political crisis inside Zimbabwe precipitated by Mugabe's decision to fire one of his two vice presidents.
Mugabe dismissed his presumed successor, Emmerson Mnangagwa, who then left Zimbabwe.
According to Reuters, military leaders saw the move as an attempt to clear the way for Mugabe's wife, 52-year-old Grace Mugabe, to take power herself.
It is unclear where either Grace Mugabe or Mnangagwa is now. The military's statement refers to Mugabe "and his family," implying that his wife is with him.
Outlets including Sky News have suggested she has fled west to Namibia, but a minister in the Namibian government has denied that is the case.
Reports online that Mnangagwa has returned to Zimbabwe have yet to be verified by any major news organisation.
The situation is coming to a head in advance of the ZANU-PF special congress next month, where Mugabe can appoint a new vice-president.
The US Embassy in Zimbabwe has advised all US citizens in Zimbabwe to stay where they are until further notice due to the country's "political uncertainty."
The US embassy and the EU embassy announced they will be closed on November 15.
The United Kingdom's embassy in Harare issued a similar warning, telling British nationals in the city to "stay safely at home/indoors until the situation becomes clearer."