Southern African leaders are meeting in Johannesburg for talks aimed at breaking Zimbabwe's political deadlock.
Zimbabwe's opposition has reportedly warned that at least a million Zimbabweans could starve to death in a year if political deadlock continues.
South Africa's new president Kgalema Motlanthe urged both sides to show "political maturity" and implement a deal agreed after disputed polls.
MDC leader Morgan Tsvangirai is said to have issued the stark warning to southern African leaders at an emergency meeting in Johannesburg.
An official said Sunday's meetings, attended by President Robert Mugabe and opposition leader Morgan Tsvangirai, would be "make or break".
Eight weeks after a power-sharing deal, the MDC and President Mugabe have still not reached agreement on a new cabinet.
Regional leaders also called for an immediate ceasefire in DR Congo.
The summit is also discussing the crisis in Democratic Republic of Congo.
The UN reported fresh fighting had broken out between rebels and government forces on Sunday near Ngungu, 60km west of the regional capital, Goma. More than a quarter of a million people have been displaced in the eastern Congo since fighting flared up in August.
The BBC's Peter Biles, reporting from the meeting, says there is little reason to be optimistic on Zimbabwe at the moment, with only five heads of state attending out of the 15 countries invited. The others were represented by lower ranking officials.
Mr Motlanthe, who is chairing the meeting the Southern African Development Community (SADC), said: "We call for an immediate ceasefire to allow humanitarian assistance to the displaced people".
'Political maturity'
"We firmly believe that there is no military solution to the problem."
South Africa's new President, Kgalema Motlanthe, who is chairing the Southern African Development Community meeting, urged both sides in the former Rhodesia to implement the deal agreed after disputed polls.
Sticking point
He said: "The political leadership in Zimbabwe owe it to the people of Zimbabwe in the region to show political maturity by putting the interest of Zimbabwe first."
The emergency summit had originally been called to tackle the Zimbabwe political crisis.
President Motlanthe says Zimbabwe can ill afford its disputes
Mr Motlanthe said he was disappointed that two months after the signing of a power sharing agreement, the parties still had not formed an inclusive government.
Mr Tsvangirai, leader of the Movement for Democratic Change (MDC), and President Robert Mugabe have been unable to agree on how to share cabinet posts.
"The political leadership in Zimbabwe owe it to the people of Zimbabwe in the region to show political maturity by putting the interest of Zimbabwe first," he said. About 1,000 people are protesting outside the summit venue
A key sticking point has been control of the home affairs ministry, which is responsible for the police.
Mr Tsvangirai, leader of the Movement for Democratic Change (MDC), and Mr Mugabe have been unable to agree on how to share cabinet posts.
Zimbabwe is facing severe food shortages and rampant inflation but neither side appears willing to compromise.
The key sticking point at the latest round of talks was control of the home affairs ministry, which is responsible for the police.
The country is facing severe food shortages and rampant inflation but neither side appears to be willing to compromise.
The summit follows a smaller meeting at the end of October, which concluded without success.
The summit follows a smaller meeting at the end of October, which concluded without success.
'Make or break'
A top Zimbabwean government official told AFP that Sunday's meetings would be "make or break".
A top Zimbabwean government official told AFP that Sunday's meetings would be "make or break".
He said that if Mr Tsvangirai and his party "continue to make outrageous demands, shifting goalposts", the ruling Zanu-PF party would go its own way, adding: "We don't care what the world will say."
He said that if Mr Tsvangirai and his party "continue to make outrageous demands, shifting goalposts", the ruling Zanu-PF party would go its own way, adding: "We don't care what the world will say."
Mr Biti said Zimbabwe was becoming an embarrassment to all AfricansMeanwhile, an opposition spokesman said that unless there was a "major shift" in Zanu-PF's position, the MDC would not accept the deal.
The Johannesburg summit called for fighting to stop in DR Congo
MDC chairman Tendai Biti said that Zimbabwe had become "an embarrassment to every African".
Meanwhile an opposition spokesman said that unless there was a "major shift" in Zanu-PF's position, the MDC would not accept the deal.
"We need to close this chapter of Zimbabwe so that Zimbabwe can reconstruct, can restart and can rehabilitate itself and can move forward," he said.
The opposition party's secretary-general, Tendai Biti, said: "We need to close this chapter so that Zimbabwe can reconstruct, can restart and can rehabilitate itself and can move forward."
The BBC's Peter Biles, in Johannesburg, says that despite the international pressure, there is little sense of optimism about the summit.
Last week, the MDC claimed that Mr Mugabe's party had unleashed "a new orgy of brutality and assaults across the whole country".
Last week, the MDC claimed that Mr Mugabe's party had "killed the dialogue" by unleashing "a new orgy of brutality and assaults across the whole country".
Amid reports of fresh clashes in the Democratic Republic of Congo, leaders at Sunday's Johannesburg summit urged rebel and government forces to uphold a fragile ceasefire.
It said a Zanu-PF militia group had attacked at least 25 MDC supporters in the capital, Harare, and that state security forces had raided homes belonging to MDC supporters, arresting nine people including a two-year-old child.
South Africa's president said: "We firmly believe there is no military solution to the problem."
The UN reported renewed fighting on Sunday around Ngungu, just west of the regional capital, Goma. More than a quarter of a million people have been displaced in the eastern DR Congo since fighting flared up in August.
A medical aid group told the BBC News website it was struggling to contain a cholera outbreak in a crowded refugee camp near Goma.
Medecins Sans Frontieres said it had treated 45 suspected cholera cases in Kibati since Friday and warned the potential for an epidemic was "a big concern".
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