• READ MORE: Robert Mugabe ‘fine’ as tanks on streets of Harare
South Africa President Jacob Zuma, speaking in parliament, said the political situation “very shortly will be becoming clear” but that it was too early to take any firm decision.
The talks include the military and, reportedly, the Catholic Church.
Seizing on the political limbo to speak out, civil society groups and opposition leaders urged Mr Mugabe to step aside after 37 years in power and for the country to transition into free and fair elections.
Mr Mugabe has been in military custody, reportedly with his wife, and there was no sign of the recently-fired deputy Emmerson Mnangagwa, who fled the country last week.
The military remained in the streets of capital city Harare. Southern African regional officials were meeting in neighbouring Botswana on the crisis.
A joint statement by more than 100 civil society groups urged Mr Mugabe, 93, to peacefully step aside and asked the military to quickly restore order and respect the constitution.
One analyst said he believed the negotiations “have pretty much reached an end point” to get Mr Mugabe to step aside and that it was a “matter of hours or days”.
Knox Chitiyo, associate fellow with the Africa programme at Chatham House, warned speculation remains high but the aim was a peaceful, managed transition.
He said the military wants a dignified exit for Mr Mugabe, who has ruled since independence from white minority rule in 1980.
Opposition leader Morgan Tsvangirai, who shared power with Mr Mugabe between 2009 and 2013, said the president must resign and that his party would participate in talks on a transitional mechanism if approached.
Joice Mujuru, a vice president who was fired in 2014, called for “free, fair and credible elections” following a transition arrangement that draws from a range of communities.
Evan Mawarire, the pastor whose #ThisFlag social media campaign last year led to the largest anti-government protests in a decade, asked: “Should we just sit and wait or shall we at least be part of this transition process?”
Across the country, Zimbabweans were enjoying freedoms they have not had in years.
Soldiers manning the few checkpoints on roads leading into downtown Harare greeted motorists with a smile, searching cars without hostilities and wishing motorists a safe journey.
Amid questions about the whereabouts of first lady Grace Mugabe, one Namibian newspaper, the New Era, reported that the country’s foreign minister denied she had fled there.
The US Embassy advised citizens in Zimbabwe to “limit unnecessary movements” as political uncertainty continues.
The UK Government also urged its citizens to avoid large gatherings and any demonstrations.