Mugabe was admired by many as a freedom fighter and African statesman who raised literacy levels in his country and improved access to health services among blacks after independence from Britain in 1980, but was reviled by many others both at home and abroad by the time he was forced to step down, accused of running what was once one of Africa's most promising economies into the ground.

Mnangagwa, currently in neighbouring South Africa for the World Economic Forum on Africa, announced Mugabe's death via his Twitter account.

"It is with the utmost sadness that I announce the passing on of Zimbabwe's founding father and former president, Cde (comrade) Robert Mugabe," he said.

"Cde Mugabe was an icon of liberation, a pan-Africanist who dedicated his life to the emancipation and empowerment of his people. His contribution to the history of our nation and continent will never be forgotten. May his soul rest in eternal peace."

Mnangagwa gave no further details, but media reports said the increasingly frail Mugabe died in Singapore, where he had frequently travelled for medical treatment over the last few years.

Mugabe, who became Zimbabwe's first black leader at independence, first as prime minister in 1980 and then as president from 1987, was once touted for investing heavily in health and education in the early years of his rule, leaving his country with one of the highest literacy rates in Africa.

"He was a colossus on the Zimbabwean stage and his enduring positive legacy will be his role in ending white minority rule and expanding a quality education to all Zimbabweans," David Coltart, treasurer-general of Zimbabwe's main opposition Movement for Democratic Change and a fierce critic of the former leader, wrote on Twitter.

Mugabe however became increasingly unpopular as the economy began to wane, later facing accusations of cracking down on his political opponents and rigging elections to stay in power. 

His government's controversial seizure of white owned commercial farms for redistribution among blacks he said had been dispossessed of the land during colonialism triggered a sharp economic meltdown in 2000 in what was once regarded as Africa's breadbasket, from which Zimbabwe has never recovered.

The fact that he sought treatment outside Zimbabwe was testimony to the collapse of the country's health system, with most hospitals and clinics unable to dispense even the most basic medication to patients.

Mugabe stepped down under military pressure in November 2017 amid infighting within his ruling ZANU-PF party which saw his deputy Mnangagwa, who was in a rival faction, take over as president.

"Regrettably the negative aspects of his legacy - violence, disrespect for the rule of law, corruption & abuse of power - live on in the new regime which overthrew him in the 2017 coup," the MDC's Coltart said on Friday.

The ruling African National Congress in South Africa, host to millions of Zimbabweans who fled political and economic turmoil back home, said Mugabe "passes away having devoted his life to the service of his country and his people".

"Though the ANC and its leadership may have differed, often vociferously, with comrade Mugabe on matters of national interest - as fraternal organizations we held as sacrosanct the principle of sovereignty," it said in a statement.

"History alone will be the decider over whether the courses of action taken by leaders in the interests of their countrymen, were the correct ones. We remember the immortal words of William Shakespeare, that the deeds men do live after them, and yet 'the good is oft interred with their bones.' "

African News Agency (ANA)