Mnangagwa, 74, fell ill at a rally where Mugabe spoke on Saturday in the southern town of Gwanda, and suffered severe suspected food poisoning.
“Some of his doctors are in South Africa,” health minister David Parirenyatwa told reporters in the capital Harare.
“He is well. He is much better, he is almost jovial. He was vomiting with diarrhoea and he became dehydrated. He has done a battery of tests.”
With Mugabe, 93, in increasingly frail health, speculation over his successor has focused on Mnangagwa, a veteran regime loyalist.
‘We need peace within our party’
Mnangagwa’s main rivals within the ruling Zanu-PF party are the younger “Generation 40” or “G40” group, which is seen as supported by Mugabe’s wife Grace, who could herself be a potential presidential candidate.
Mugabe, who often travels abroad for medical treatment, has refused to name a successor and repeatedly denounced factionalism in the party.
“Vice President Emmerson Mnangagwa is not yet back from hospital in Johannesburg,” Mugabe said in a speech on Monday without giving details.
Zimbabwe is due to hold elections next year, with opposition parties in talks to try to unite and field one candidate to oppose Mugabe.
Past elections have been tainted by violence and intimidation by Zanu-PF operatives.
“We hope the election exercise will be done in peace,” Mugabe said.
“We need peace within our party. We need peace between our party and others. We need national peace in our country.”