More than six million North Koreans will go without emergency food aid until April, says the UN.
Only the most vulnerable will continue to receive aid
The UN World Food Programme (WFP) says it has run out of food and blames the supply shortfall on a funding crisis.
For the next two months food rations will only be given to 100,000 people - mostly child-bearing women and children in hospitals and orphanages.
A quarter of the population who normally receive food aid will have to survive winter without normal rations.
Food shortages have plagued North Korea for at least nine years, after floods, economic mismanagement and the consequences of the break-up of chief donor the USSR combined to precipitate the crisis.
WFP Pyongyang representative Masood Hyder said the agency was scraping the bottom of the barrel.
"If you're going to give, please give early," was Mr Hyder's message to donor countries.
He said the crisis had come at the "wrong time", when harvest stocks were already depleted and recent economic reforms had forced up prices on farmers' markets.
'Solution or problem?'
Mr Hyder blamed the funding shortfall on an unfavourable political context - a reference perhaps to North Korea's nuclear ambitions, says the BBC's Louisa Lim in Beijing - and donor fatigue with a country which has received food aid for nine years.
Mr Hyder said he hoped six-nation talks on the nuclear crisis could change this.
NORTH KOREA'S AID CRISIS
In need of aid:
2.7m other children
0.3m pregnant/nursing women
0.7m elderly people
350,000 low-income households
190,000 teachers and carers
He responded to the charge that assistance from the WFP was contributing to a dependence on aid in North Korea.
"Whenever humanitarian action is protracted these kinds of worries arise: 'Are we the solution or have we become part of the problem?'" he told the BBC World Service's World Today programme.
"I think we've got to be quite robust in confronting these issues - so long as there are people in need ... there is a strong case for the WFP to assist."
The WFP representative said the current pattern of stop-go had begun in September 2002.
The worst until now had been an inability to feed half the people on the WFP's books.
"Now we're talking of a total cutback," Mr Hyder said. "It's graver, with deeper consequences."
"Right now we are in the situation where we will be unable to feed all 6.5million, perhaps we will be able to feed just under 100,000 in February and March, but the vast majority we will not be able to help," he said.
Mr Hyder described the consequences as a real increase in suffering and malnourishment.
"People are not really expected to die because of the short-term deprivations," he said. "People in fragile and recovering health... would then again suffer a setback."
Underweight pregnant mothers were more likely to give birth to poorly developed babies, and many elderly people would be unable to buy food at the markets.
Though the US, Russia and other countries had pledged thousands of tonnes of grain and other food, the next shipments of aid will only arrive in North Korea in April.
The WFP says it will face another crisis from June onwards.