One in eight people around the world is chronically undernourished, the United Nations' food agencies has warned.

In their latest report on food insecurity, the UN agencies estimated that 842 million people were suffering chronic hunger in 2011-13, 12 per cent of the world's population.

The figure was down 17 per cent from 1990-92 and the new total was lower than the last estimate of 868 million in 2010-12 and 1.02 billion in 2009, but the bodies said progress was uneven in meeting the Millennium Development Goal to halve hunger by 2015.

Many countries were unlikely to meet the goal adopted at the United Nations in 2000, said the Food and Agriculture Organisation (FAO), the World Food Programme (WFP) and the International Fund for Agricultural Development (IFAD).

"Those countries that have experienced conflict during the past two decades are more likely to have seen significant setbacks in reducing hunger," the groups' report said.

"Landlocked countries face persistent challenges in accessing world markets, while countries with poor infrastructure and weak institutions face additional constraints."

FAO, WFP and IFAD define undernourishment in the State of Food Insecurity in the World 2013 report as "not having enough food for an active and healthy life" and an inability to "meet dietary energy requirements."

Policies aimed at boosting agriculture and food availability were crucial in reducing hunger even where poverty was widespread, the agencies said.

"When they are combined with social protection and other measures that increase the incomes of poor families to buy food, they can have an even more positive effect and spur rural development," they said.

The vast majority of people suffering hunger - around 827 million - live in developing countries, where undernourishment is estimated at 14.3 per cent.

Africa remains the region with the highest proportion of undernourished people, with more than one in five estimated to be undernourished. The majority of undernourished people are in southern Asia.