President Robert Mugabe under house arrest. A Roman Catholic priest known to him for years is trying to mediate a deal on his future with the military.
South African ministers have been in the capital Harare meeting the army and political parties.
The Southern African Development Community (SADC) regional bloc is to hold emergency talks shortly.
President Mugabe, 93, has been in control of Zimbabwe since it threw off white minority rule in 1980.
However, the power struggle over who might succeed him, between his wife Grace Mugabe and her rival, former Vice-President Emmerson Mnangagwa, has split the ruling Zanu-PF party in recent months.