Kgalema Motlanthe, South Africa's president, was set to mediate Monday's talks, joined by Thabo Mbeki, his predecessor, and Armando Emilio Guebuza, Mozambique's president.
The bid to ease political deadlock comes amid a backdrop of hyper-inflation in the country that has seen prices doubling daily, and an epidemic of cholera that has killed more than 2,000 people.
"The economy in Zimbabwe is crumbling, with [the] highest inflation rate in the world, at 231 million per cent"
Ann Veneman, head of Unicef
Doctors and nurses at public hospitals have been on strike for months, demanding higher wages as the inflation has essentially rendered their salaries useless.
The UN Children's Fund (Unicef) pledged $5 million for the ailing health sector on Saturday.
Ann Veneman, the head of Unicef, speaking in Harare, warned that the cholera epidemic, which broke out in August, has yet to be controlled and urged aid workers to put "children on the forefront of their collective agenda".
"Over half the population is receiving food aid, health centres have closed, and when the school term starts there is no guarantee that there will be enough teachers," she said.
"The economy in Zimbabwe is crumbling, with [the] highest inflation rate in the world, at 231 million per cent."
Zimbabwe's central bank announced on Friday that it was issuing a 100 trillion Zimbabwean dollar note, worth about $33 on the black market, to try to ease currency shortages.
But previous issuances of banknotes worth ever-larger sums have done little to ease an economic crisis that has led to widespread food and fuel shortages.
Critics have blamed the turmoil on government mismanagement, including the post-revolutionary seizure and redistribution of thousands of white-owned farms, which has seen the once-thriving farm sector fall into ruin.
Mugabe, 84, who has ruled Zimbabwe since the country gained independence from Britain in 1980, blames the country's problems on Western sanctions and interference.
Analysts say the establishment of a unity government may be the best hope of reversing the country's economic and humanitarian crises.