The world food crisis will have serious knock-on effects in years to come, the U.N. humanitarian chief said this week, echoing experts' warnings of a "silent rolling tsunami".

John Holmes, the U.N. Under Secretary General for Humanitarian Affairs, said the steep hike in food prices, which has already triggered unrest around the globe, had the potential to create conflict and political instability.

But he also said the crisis was a great opportunity to overhaul global agriculture which would in the long run bring major benefits to the developing world.

Holmes said it was too early to judge the scale of the food crisis, but that it didn't look like "a classic Ethiopian famine scenario with people dying of starvation in large numbers in one place".

"It's rather more insidious than that. People have described it as a silent rolling tsunami and I think that's quite a good analogy," he told Reuters AlertNet.

"In other words you have hundreds of millions of people who are eating less, and eating less well. This will have a dramatic effect ... because if you are malnourished as a young child you will never recover from it mentally or physically."

On top of that, if parents have to spend more on food, they will be forced to cut back on their children's healthcare and education, further harming the next generation's ability to prosper later in life.

"The knock-on effects are enormous and probably accumulating as we speak. We have not seen the effects of this crisis yet," Holmes said.

Holmes warned that aid agencies may for the first time have to help large numbers of urban poor as opposed to the rural populations they usually assist in conflicts and natural disasters.

"People in large cities may be the worst hit because they are totally dependent on buying food. They do not have farms or subsistence."

One of the main challenges will be identifying the most vulnerable people in large cities. Another will be distributing aid in crowded neighbourhoods where only the most needy will get help. This could create security risks you wouldn't get in rural areas.

"The risks are greater and they are not risks we are particularly familiar with. We need to learn some new techniques and practices to make sure we can cope with that," Holmes said.

BIOFUELS NOT ALL BAD

The price surge has been blamed on factors including increased food demand from rapidly developing nations such as China, market speculation and the rising use of food crops for biofuels.

But Holmes said the world should not "throw out the baby with the bathwater" when it came to biofuels which have been touted as a green alternative to fossil fuels.

"We need to see where it makes sense to use agricultural products for energy products and where it makes sense to use them for food, rather than saying that all biofuels are by definition bad.

"We were trying to solve a very serious problem with biofuels which has not gone away. Climate change is the biggest problem we face ... and it's a more difficult problem (to resolve) than food production."

With the right mix of policies, Homes predicted that food production could be sorted out in three to five years.

Although the crisis will increase poverty in developing countries in the short term, Holmes said it could be beneficial in the long term if the world seized the chance to revitalise agricultural production and trade. Western farming subsidies, which squeeze farmers in poor countries out of the market, should be part of the discussion, he said.

"There are opportunities here as well as dangers to look at this with a fresh eye ... Farmers in the developing countries could be the big beneficiaries if you can get more investment in agriculture," Holmes said.

"And if farmers in the developing countries are producing profitably and bringing more land into use that's very good for the world's poor."

Holmes distanced himself from comments made last week by U.N. food envoy Jean Ziegler who said the food price hikes were leading to "silent mass murder".

"I think that's a little over the top ...describing it in the way he has is unhelpful and is not a description I would use," he said.

He also cautioned against any scaremongering, saying this could exacerbate problems.

"I think it's important not to be too alarmist about this situation because it's not going to help, frankly. We want to avoid reactions which may be unhelpful like hoarding or panic buying, or unhelpful reactions by individual countries in terms of export bans or export tariffs imposed on their usual food exports."

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