UN projects that could be affected include those which provide shelter, food, water and medical aid, and those that clear landmines and help people improve their agricultural output.
Holmes noted that the $4.6bn collected in the first half of the year "is the best ever result we've had at mid year and particularly, I think, noteworthy because of the economic and financial crisis that we're all going through".
But he said there were more people in need across the world at the moment, and more crises, so more funding was needed.
"Those overall requirements are the highest ever at mid-year, and that means the needs still to be funded, at around $4.84bn, are also the highest we've ever had," he told journalists in Geneva.
New crises
New crises this year, including in Sri Lanka and Pakistan where conflicts have displaced hundreds of thousands of people, mean the UN relief agency expects to help 43 million for the year, a more than 50 per cent jump from last year's 28 million.
The effects of climate change - such as droughts – on agricultural production are hitting the poorest nations hard, such as those in Africa.
That and civil war on the continent have pushed more below the poverty line and led to African nations topping the list of those suffering the most, including Sudan, the Democratic Republic of Congo, Zimbabwe and Somalia.
Eric Munoz, who is the co-author of the 2009 World Hunger Report and represents the Bread for the World Institute, told Al Jazeera that there needs to be "a major aid push just to address immediate suffering".
Looking long term
But he added that "we need to figure out ways in the long term to deal with the structural issues that keep people in poverty".
"We have had a long history - decades worth - of ignoring agriculture in developing countries and we are sowing the legacy of that right now.
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| The UN expects to assist 43 million of the world's poor this year [EPA] |
"A return to agriculture and a return to investments in rural infrastructure ... is absolutely essential."
On the question of whether aid was counter-productive, Munoz said while "studies vary on the effectiveness of aid on assisting with economic development … aid has had a tremendous impact on ridding the world of smallpox, on lowering child mortality rates around the world, on putting millions of people on anti-retroviral drugs to address HIV/Aids".
Holmes said the global economic crisis was affecting the poor, but "the main contributing countries have stuck to their promises which was to maintain their aid budgets, both development and humanitarian budgets, despite the recession".
"They have certainly done that so far this year, and I very much hope it continues," he added.
Coverage of the total needs in recent years has sometimes been as low as 23 per cent after six months, and last year donor nations had provided $2.9bn or 46 per cent of the UN's annual relief budget over the same period.