By David Loyn
International development correspondent, BBC News
The head of the World Food Programme (WFP), Josette Sheeran, says the world may be reaching a point where the global system can no longer cope with the number of hungry people.
Riots over sharply rising food prices struck a number of countries last year
"What we may be witnessing is a fundamental breakdown in food markets in a way that does not allow nations to feel secure that they can produce or purchase enough food to be able to feed their populations," she told the BBC at a UN emergency food summit in Madrid.
After food prices rose last year the WFP found itself with 30 million more mouths to feed.
The number of people in the world defined as "hungry" is now close to one billion for the first time.
And Ms Sheeran's fears of imminent collapse have been fuelled by a group of factors that she says could mean that the challenge this year will be at least as great as during the food price crisis a year ago.
Food prices may be lower than at the peak then, but remain volatile with world grain prices now around 80% higher than they were four years ago.
One of the effects of the world financial slowdown has been to cut the amount of money sent back by overseas workers to some of the poorest countries.
The lower availability of credit for some middle-sized Asian economies like Malaysia and the Philippines makes it harder for them to ensure food security. Meanwhile, countries dependent on commodity exports are suffering as prices fall.
Ms Sheeran said that a new "hunger map" has discovered need in some unexpected places.
Kyrgyzstan, a Central Asian republic that has not needed food aid since the collapse of communism in the early 1990s, is now asking for help again.
Meanwhile, the existing pressures on food prices have not gone away. These include volatile oil prices, climate change and competition from biofuels for scarce land.
Opening the conference, the head of the UN's Food and Agriculture programme, Jacques Diouf, said food prices would go up again if there were not more investment in agriculture after 20 years when this has been falling.
Professor Jeffrey Sachs, who produced a paper for the conference recommending new measures to help African farmers, said that because of the worldwide economic crisis there is a possibility that not enough crops will be planted in Africa again this year.
He said that $10bn (£7.2bn) will be needed every year to ensure that Africa can feed itself, alongside the further $5bn needed to provide increased food aid.
Echoing the words of the UN Secretary General Ban Ki-moon, Ms Sheeran said that after the trillions spent to help those on Wall Street and on Main Street, "Five billion dollars for the places with no streets to make sure that the most severe human suffering does not happen, does not seem out of line.
"The world needs to be sure of its priorities. Making sure that there is adequate food has to be a top priority. This is an issue of human compassion, but beyond that has to be about peace security and stability," she said.