Flooding and poor harvests have caused North Korea's worst food crisis since the late 1990s and have put millions at risk, the United Nations' food agency said Wednesday.

The food shortage threatens widespread malnutrition, the World Food Program said.

"Millions of vulnerable North Koreans are at risk of slipping toward precarious hunger levels," Jean-Pierre de Margerie, the WFP's country director for North Korea, told a news conference.

The WFP had been given permission to launch a new operation to target those most vulnerable in eight of the country's 10 provinces, or 6.4 million people, up from a current 1.2 million.

An international appeal for aid would be launched in the next two weeks. Food aid is needed to tide people over for the next three to four months until the next harvest, he said.

While 400,000 metric tons of U.S. food aid have already shipped, there is an urgent need for $20 million to get through the next autumn harvest, de Margerie said. "We are running against the clock here," he said.

The North has resorted to outside handouts to help feed its 23 million people since the mid-1990s when natural disasters and mismanagement devastated its centrally controlled economy. An estimated 2 million people died of hunger at the time.

But outside aid has fallen this year, de Margerie said, compounded by domestic shortfalls.

The amount of food given in government rations to urban dwellers has fallen in the last few months, as prices for staple goods have risen dramatically due to less internal transfers of food.

Rice now costs almost three times more than it did a year ago, he said, and maize has quadrupled. But salaries for Koreans have remained stagnant.

The WFP's food security survey, the first since 2004, interviewed over 250 households in 53 counties across eight provinces, and found that people are running out of options, de Margerie said.

Many are relying on relatives to supply food, or have set up gardens in their kitchens or on steep mountainous hillsides, he said. Some are scavenging for wild foods. Nearly three quarters of households have reduced their food intake.

"People are starting to exhaust their coping mechanisms," he said. "That's why it's critical for us to mobilize food right now."