North Korea has slashed food rations by two-thirds and desperately needs foreign aid to feed millions of people, the UN humanitarian chief said Friday after visiting the communist state.

Donations to United Nations programmes have dwindled because of international irritation at the impoverished North's missile and nuclear push.

UN agencies have said that some six million people in the country urgently need food but a $73 million appeal for North Korea has only been 34 percent funded this year.

Valerie Amos urged foreign donors to give more as the harsh winter approached.

"There are real needs there, you can't let the people of North Korea suffer," Amos told journalists in Beijing after a five-day visit to inspect the humanitarian situation in North Korea.

"This is a country that is chronically poor and underdeveloped. There is no way, even with the best will in the world and best climate conditions, that the DPRK (North Korea) can feed itself."

Amos said this year's harvest was "about the same or slightly better" than in 2010, but it was still not enough to feed the population of 24 million people.

While the lack of arable land was partly to blame, Amos said other problems were soil degradation, poor quality seeds, limited fertiliser, adverse weather conditions and the lack of machinery to help harvest the crops.

North Korea faces an annual food deficit of one million tonnes and around a third of its children are chronically malnourished, said the UN under-secretary-general for humanitarian affairs.

The situation is even more dire in the country's north, where nearly half the children don't get enough food.

North Korea was hit by a famine in the 1990s which killed hundreds of thousands and the islolated country has relied partly on international food aid ever since.

But humanitarian support has fallen to a tenth of what it was a decade ago and Amos said daily food rations at government distribution centres had been cut from 600 grams to just 200 grams.

The rations were mostly maize, cabbage and rice "if they are lucky" with little or no protein provided.

Seoul suspended its annual shipment of rice and fertiliser in 2008. This year the North asked the United States and other nations for food aid, but there are differences over its requirements.

Some South Korean officials are sceptical, saying North Korea wants to stockpile supplies for handouts to mark the 100th anniversary next year of the birth of founder Kim Il-Sung.

Many governments have also raised concerns that food aid could be diverted to the North's 1.1-million-member army.

Amos said she saw no signs of food being diverted on her visit, during which she had "very frank discussions" with North Korean officials, who said they wanted to attract more foreign investment.

Amos said she was given access to "all the places I asked to see" which included orphanages, hospitals, markets, a food distribution centre and a communal farm.

However, better access for all humanitarian organisations, not just UN agencies, in North Korea was needed, she added.