North Korea has cut food rations to 300 grammes a day, the lowest ever for this time of year, and further cuts are likely after the worst harvest in a decade, the United Nations has said.

The UN carried out a food assessment at the request of North Korea from 29 March to 12 April.

It was granted wide access, including to cooperative farms, rural and urban households, nurseries and food distribution centres.

"This new food security assessment ... has found that following the worst harvests in 10 years, due to dry spells, heat waves and flooding, 10.1 million people suffer from severe food insecurity, meaning they do not have enough food till the next harvest," World Food Programme (WFP) spokesman Herve Verhoosel said.

The survey found North Korean protein intake to be very low, with some families consuming protein only a few times a year.

The WFP and the UN Food and Agricultural Organization, which jointly carried out the survey, are among the few aid agencies with access to North Korea, which suffered a famine in the mid-1990s that killed as many as three million people.

Agricultural output of 4.9 million tonnes, the lowest since 2008-2009, had led to a food deficit of 1.36 million tonnes in the 2018/2019 marketing year, the report said.

The 10.1 million people who needed food aid included 7.5 million of the 17.5 million North Koreans who depend on government rations and 2.6 million collective farmers.

"Prospects for the 2019 early season crops of wheat and barley are worrisome, with communities at risk as the lean season gets under way in June. The effects of repeated climate shocks are compounded by shortages of fuel, fertiliser and spare parts crucial for farming," Mr Verhoosel said.

The WFP plans another assessment during July and August to understand the full extent of the crisis.