President Mugabe has been in power since 1980
Zimbabwe's envoy to South Africa, Simon Moyo, has denied as "wishful thinking" reports that President Robert Mugabe is in hospital in South Africa.
"He (Mugabe) is chairing a cabinet meeting as we speak," Mr Moyo told SAPA news agency.
"There is nothing wrong with his health."
South African Foreign Ministry spokesman Ronnie Mamoepa also denied the media reports.
"President Mugabe is not in South Africa. If he was the government would have been the first to know," he told Reuters news agency.
Their comments followed media reports quoting unnamed sources in Zimbabwe as saying that Mr Mugabe had collapsed on Monday and had been flown to South Africa for emergency medical treatment.
Correspondents say there have been a number of rumours about Mr Mugabe's health in recent years.
Mr Mugabe has been in power in Zimbabwe for 23 years.
He was re-elected president last year amid allegations of widespread vote-rigging and continued human rights abuses.