Floods in North Korea that have left hundreds dead or missing are the "worst disaster" to hit the country since World War II, state media said on Wednesday.

The official KCNA news agency did not give exact numbers of those killed or unaccounted for, but a UN report said 138 people have died and 400 are missing after torrential rains caused devastation in the country's far north.

The floods along the Tumen River, which partially marks the border with China and Russia, tore through villages, washing away buildings and leaving thousands in urgent need of food and shelter.

"The flood that resulted from the typhoon that hit North Hamgyong province from August 29 to September 2 was the worst disaster since liberation from Japanese colonial rule in 1945," KCNA said.

It also provided figures on the flood damage and those displaced for the first time, saying 68,900 people had been forced to flee their homes, compared with a UN figure of 107,000.

At least 29,800 homes and 900 public buildings were destroyed, it said, adding that 180 sections of road and over 60 bridges had been severely damaged, and electricity and communication lines were cut.

But the report trumpeted the role of North Korea's ruling Workers' Party in responding to the disaster, saying all efforts were being put into rebuilding the northeastern border region, and that the military and people had responded to government calls to join rescue efforts.

Impoverished North Korea is vulnerable to natural disasters, especially floods, as mountains and hills that have long been stripped bare for fuel or turned into terraced rice fields allow rainwater to flow downhill unchecked.

However, huge government resources are swallowed up by a missile and nuclear weapons programme that Pyongyang says is essential to deter what it considers US aggression.

A series of floods and droughts was partially responsible for a famine that killed hundreds of thousands between 1994-98, with economic mismanagement and the loss of Soviet support exacerbating the situation.

The UN Food and Agriculture Organization said in April that North Korea's chronic food shortages were expected to worsen, due to tight food supplies last year and this year when "most households were already estimated to have poor or borderline food consumption levels".

The United Nations Security Council is also planning fresh sanctions against the North after it staged its fifth nuclear weapons test last week.