A member of Zimbabwe's military read out a statement on the country's national broadcaster, ZBC, saying it has taken action to "target criminals".
The streets of Zimbabwe's capital Harare were eerily quiet on Wednesday morning but wartime songs were broadcast over state radio and TV stations, while soldiers stopped pedestrians and motorists to ask for identity documents, witnesses say.
The leader of Zimbabwe's influential liberation war veterans called Wednesday for South Africa, southern Africa and the West to re-engage with Zimbabwe after the military seized power from 93-year-old President Robert Mugabe.
Two hours later, soldiers overran the headquarters of the ZBC, and ordered staff to leave.
"We want to assure the nation that His Excellency the President of the Republic of Zimbabwe and Commander-in-Chief of the Zimbabwe Defence Forces, Cde R.G. Mugabe and his family are safe and sound and their security is guaranteed", Moyo said.
In response to the conference, Mugabe's political party accused Chiwenga of "treasonable conduct". Tanks were seen advancing towards Harare late yesterday afternoon.
"As a country that is friendly with Zimbabwe, we are paying close attention to developments of the situation in Zimbabwe", Geng added.
The activity triggered speculation of a coup, but the military's supporters praised it as a "bloodless correction".
The public dispute has presented a major test for President Mugabe, who is in increasingly frail health.
Zimbabwe's President Robert Gabriel Mugabe addresses the U.N. General Assembly at the United Nations on September 21, 2017, in New York, New York.
The US embassy in Zimbabwe has told American citizens in the country to "shelter in place".
Mnangagwa had previously been seen as Mugabe's successor but was replaced by the president's wife, Grace Mugabe, as the favorite, resulting in a split in the Zanu-PF.
Mugabe's second wife has developed a reputation as a shrewd, if sometimes extravagant, politician, and has steadily gained influence among youth in Zimbabwe.
"Defending the revolution and our leader and president is an ideal we live for and if need be it is a principle we are prepared to die for", Kudzai Chipanga, who leads the ZANU-PF Youth League, said at the party's headquarters in Harare.
The general was talking about a recent shuffle in the party.
In an address to the nation, an army spokesman said the military is targeting "criminals" around Mugabe, and sought to reassure the country that order will be restored.
Last week, Mugabe fired his vice president.