The head of the World Food Programme says the current food shortages in Zimbabwe make it one of the countries he is most worried about in the world.
House demolitions were condemned by the UN Security Council
James Morris said the WFP would help distribute food, but only if it did not have interference from the government.
He told the UN Security Council "the greatest humanitarian crisis we face today" was not in Darfur, Afghanistan or North Korea, but in southern Africa.
Council members used the debate on hunger in Africa to criticise Zimbabwe.
Mr Morris told the Council that the disintegration of social structures in southern Africa and the accompanying hunger meant it was the world's worst humanitarian crisis.
"A lethal mix of Aids, recurring drought and failing governance is eroding social and political stability," he said.
The number of people needing emergency food aid had doubled since the beginning of the year to eight million because of the return of drought to some areas, he pointed out.
"More than four million people are at risk in Zimbabwe, 1.6 million in Malawi, 1.2 million in Zambia, and 900,000 in Mozambique," he warned.
'Bad policies, bad governance'
Mr Morris said he had told President Robert Mugabe on a recent visit to Zimbabwe that the WFP would help with food distribution, but only if it was allowed to operate freely without government interference.
He said he was told the government wanted to feed its own people.
Mr Morris said he pressed his concerns in talks with Mr Mugabe
"We've made it very clear what our operating principles are, that we have to have full access to the people throughout the country," Mr Morris said.
The Security Council discussion on Africa's food crisis gave members a rare opportunity to publicly discuss Zimbabwe.
In particular, they criticised the government's policy of demolishing houses which has left hundreds of thousands of people homeless.
Mr Mugabe argues that the demolitions are needed to root out criminals involved in black market trading and to regenerate cities.
Britain's ambassador to the UN, Emyr Jones-Parry, said the government was to blame for many of the problems facing Zimbabwe.
"It's important to realise that this particular crisis has been caused by the Zimbabwean government," he said.
"It is man-made and not a natural phenomenon. The economic collapse in Zimbabwe is the result of bad policies and bad governance."
Acting US ambassador Anne Patterson said America was deeply concerned about the demolition scheme.
She urged Zimbabwe's government to begin a dialogue with the opposition to help reverse the economy's continuing decline.