Soldiers in armored vehicles have stationed themselves at key points around Zimbabwe's capital, Harare, with the army saying it was not "a military takeover."
In a statement read out on national television, a military spokesman said on November 15 that the military took action to "target criminals" around 93-year-old President Robert Mugabe.
It did not name those targeted.
South Africa’s presidency said President Jacob Zuma spoke to Mugabe, who "indicated that he was confined to his home but said that he was fine."
During the night, explosions and gunfire were heard in Harare.
The U.S. Embassy advised U.S. citizens to stay at home due to "ongoing political uncertainty." The British Embassy issued a similar warning, citing "reports of unusual military activity."
The latest events came after Zimbabwe's ruling party accused the country's army chief of treason amid a row over Mugabe’s succession.
Last week, Mugabe sacked Vice-President Emmerson Mnangagwa, who was seen as an heir to the president.
The move left Mugabe's wife Grace, 52, in prime position to succeed her husband.
Mugabe, the world's oldest head of state, has ruled since independence from white-minority rule in 1980.