Millions are facing starvation this winter
Mr Annan said that Afghanistan and its neighbours have seen a 50% increase in the number of people relying on aid for survival, from five million to 7.5m people.
Earlier UK Prime Minister Tony Blair called for a "humanitarian coalition" to help the people of Afghanistan, saying that international aid to tackle the effect of years of war and famine must go alongside any military action.
Click here for map of Afghanistan
Almost half the money being sought by the UN - $273m - will go to the UN refugee agency to handle an increase of 1.5m people who are expected to flee Afghanistan amid fears of impending US attacks.
Another $188m is earmarked for food aid.
"The crisis in Afghanistan is already serious, but we also have to be ready to deal with extra dimensions of the crisis," Mr Annan said as he launched the appeal.
Millions of Afghans were already dependent on outside aid
for their survival after decades of war and three years of
severe drought
The situation worsened when foreign aid workers left the country as the US threatened retaliation against the Taleban for harbouring Osama Bin Laden, the man suspected of masterminding the terror attacks in America.
Air drops
Pakistan and Iran are already hosting 3.5 million Afghan refugees - the largest refugee group in the world.
But while thousands have been heading for surrounding countries, most Afghans are too poor and hungry even to be able to travel to the international borders, the BBC's Afghanistan correspondent Kate Clark says.
Aid agencies are saying that up to eight million people inside Afghanistan are now expected to need food aid this winter.
Noting that most UN staff had already left Afghanistan, Mr Annan said "we may have to consider air drops" to deliver food.
Earlier British Prime Minister Tony Blair stressed the need to build a humanitarian coalition to tackle the crisis, insisting that the fight was against terrorism not the Afghan people.
"Our fight is not with Islam or with the people of Afghanistan. Our fight is with those who planned these terrible atrocities and those who harbour them," he said.
Related to this story:
Analysis: Afghanistan's future
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Blair calls for aid alliance
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Afghans brace for US strike
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Afghan refugees' unending plight
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Pakistan's fear of refugee flood
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Pakistan warns of Afghan instability
(25 Sep 01 | South Asia)
The wild border town of Quetta
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Afghans place hopes in UN
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International Federation of Red Cross |
World Food Programme |
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