Around 2.7 million people on North Korea's west coast will run out of food in October, the World Food Program said in a report released on Tuesday.
North Korea has relied on aid to help feed its 23 million people since natural disasters and mismanagement devastated its centrally controlled economy in the mid-1990s. Famine is believed to have killed 2 million people. The country's food shortage has worsened this year following devastating floods in 2007.
The WFP also said the food shortages have especially affected urban households in areas with low industrial activity due to higher food prices, reductions in public food rations and lower employment.
The food shortage warning comes as the North has ratcheted up its hostile rhetoric against South Korea and its president amid fraying ties.
In August, the WFP asked South Korea to provide emergency aid to North Korea to help it avert a food crisis, but Seoul has not yet responded.
The South Korean government said it would not tie food aid to North Korea's nuclear disarmament, but it also said public opinion was a consideration in deciding whether to send aid.
On Thursday, Unification Ministry spokesman Kim Ho-nyeon said no decision had yet been made.
South Korea has been a main aid donor to its impoverished northern neighbor, but public sentiment has worsened following the July shooting death of a South Korean tourist at a North Korean mountain resort.
North Korea had previously rejected South Korean offers of direct food aid in apparent anger over the new South Korean government's harder-line policy toward the North.
The North warned Seoul last week that it might cut any remaining ties between the neighbors if South Korea continues its policy of "reckless confrontation."
On Wednesday, South Korea denied it had taken a hard-line stance toward the North, calling that view "preconceived or biased."