North Korea is experiencing a "major and complex disaster" the Red Cross has warned, after floods killed scores of people and left tens of thousands in need of urgent help.

Rescue workers are struggling to reach stricken communities in the country's far north, where thousands have been left homeless, and the risk of disease is looming.

"From what we saw, it is clear that this is a very major and complex disaster," said Chris Staines, who heads a Red Cross delegation in North Korea and has visited the affected areas.

At least 133 people are known to have died after torrential rains triggered massive floods that tore through villages, devastating entire communities and washing away buildings.

Hundreds more are missing and 140,000 people are in urgent need of food and shelter.

"The floods came through with such force, they destroyed everything in their path," Staines said.

"People were salvaging whatever possessions they could from piles of debris that used to be their homes."

Some 24,000 houses have been totally destroyed and thousands more damaged, with the full extent of the disaster still emerging as rescue workers battle to reach areas that have been totally cut off, the Red Cross said.

"There was barely a building left unscathed," in some villages they visited on the outskirts of Hoeryong City, Staines said.

"People displaced from the floods are now in a very difficult situation and there are real risks of secondary disasters, particularly relating to people's health," Staines added.

Photographs released by the UN Children's Fund showed fields of crops destroyed by the flooding of the Tumen river, which forms the border with China, and damaged one-storey houses in a rural area of Hoeryong, in North Hamyong province.

A local Red Cross worker was shown surveying the damage as a group of North Koreans sat among a sea of mud and debris in the pictures UNICEF said were taken on September 7.

At least 100,000 people in Hoeryong City do not have safe drinking water, with up to 600,000 people in the affected area facing disruptions to their water supply, the Red Cross said.

The disaster is set to worsen North Korea's already chronic food shortages, with around 16,000 hectares (40,000 acres) of farmland inundated just weeks before the local maize and rice crops were due to be harvested.

"Their loss is another disaster that will be felt in the coming weeks and months," the Red Cross warned.

The impoverished nation is vulnerable to natural disasters, especially floods, due partly to deforestation and poor infrastructure.

At least 169 people were killed by a massive rainstorm in the summer of 2012.

Major state resources are swallowed up by a missile and nuclear weapons programme which Pyongyang says is essential to deter US aggression.