The appeal, part of a record $7 billion worldwide humanitarian appeal for 2009 announced in Geneva last week, is the highest ever for Zimbabwe and compares with just under $400 million sought a year ago.
A chronic economic crisis, including hyperinflation, has led to what U.N. Secretary-General Ban Ki-moon on Tuesday called a "desperate" situation in the southern African country. Zimbabwe is also paralyzed politically, with rival parties so far unable to agree on the make-up of a unity government.
Catherine Bragg, U.N. deputy humanitarian chief, told reporters some 60 percent of the Zimbabwe appeal was for food.
"We do encourage and appeal to donors for the generosity, and continuing generosity, to deal with this very serious situation," she said. "We assure donors that the aid is going through. We are able to reach the 3 million beneficiaries who are in need of aid at the moment."
Bragg said the 2008 appeal had been three-quarters funded by donors, but due to increasing needs during the year was likely to face a shortfall of $180 million to $200 million.
The United Nations has been warning for months that the food crisis in Zimbabwe is likely to peak between January and April, with up to 5 million people hungry.
"Without massive international assistance this situation is going to get much, much worse," Bragg said.
She said the high mortality rate of a cholera outbreak that so far has hit nearly 9,000 people and killed 366 was because communities had no clean water due to a lack of chemical treatment, and because the health service had collapsed.
The World Health Organization is procuring emergency stocks to run cholera treatment centers for one month, U.N. spokeswoman Michele Montas told a separate news briefing.