North Korea has made a rare admission that the country faces food shortages and needs help from outside, an aid official has said.
South Korea has resumed some aid shipments to the North
Pyongyang has asked the World Food Programme to expand its assistance to meet the gap, the WFP's regional director Tony Banbury said.
In recent years, the North has cut back the work of the WFP and other agencies.
Meanwhile, South Korea has announced it is sending medical aid to help the North fight a foot-and-mouth outbreak.
Seoul has also restarted shipments of fertiliser aid and humanitarian aid for victims of last year's floods.
Returning from a six-day visit to North Korea, Tony Banbury said he had been told by the country's officials that there was a food shortfall of one million tonnes.
This amounts to about 20% of the food needed by North Korea each year to feed its 23 million people.
Mr Banbury appealed for international donors to help the WFP deliver the necessary food aid.
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"Right now we are losing the fight against hunger in [North Korea]," he said.
"If donors do not respond to the request, millions of people are going to go hungry."
The World Food Programme used to feed around 6.5 million people in North Korea each year.
In 2005, its work was scaled back after the North Korean government imposed restrictions on the monitoring and distribution of food.
But the WFP has struggled to feed even half of the 1.9 million people it is still trying help, because of a drop in donations as a result of North Korea's nuclear programme.
North Korea's shortfall in food supplies was exacerbated last year when an estimated 100,000 tonnes worth of crops were washed away by the floods.
Regular shipments of food aid by South Korea were also suspended after the North carried out a missile test last July and then a nuclear test in October.
Seoul says it will not resume its deliveries until the North meets a mid-April deadline to "shut down and seal" its only operational nuclear reactor Yongbyon, as part of a deal agreed in February.
However, it has begun despatching other aid, including the first shipment of some 300,000 tonnes of fertiliser to be sent by June.
The South has resumed shipments of rice, cement, trucks and blankets to help the thousands of people who lost their homes and livelihoods in last August's floods.
It is also sending medicines and equipment to help its northern neighbour tackle an outbreak of foot-and-mouth on a farm near the capital Pyongyang, which has led to the destruction of thousands of livestock.