Thousands of women and children fleeing bloodshed in Central African Republic are arriving in Cameroon malnourished and dangerously ill, the heads of two of the biggest U.N. agencies said on Wednesday, in an appeal for donor funds.

Central African Republic has been mired in ethnic and religious violence since northern Seleka rebels, most of them Muslim, seized power in the mainly Christian country in 2013.

The Seleka left power in January under international pressure after 10 months of looting and fighting that led to the formation of Christian militias known as anti-balaka, who have carried out retaliatory attacks on Muslims.

The conflict has killed thousands of people and uprooted nearly a million.

Almost 90,000 people have fled to neighbouring Cameroon since December and up to 2,000 a week, mostly women and children, are still crossing the border, the United Nations said.

"Women and children are arriving in Cameroon in a shocking state, after weeks, sometimes months, on the road, foraging for food," said Ertharin Cousin, executive director of the World Food Programme (WFP).

"We must intervene to save lives and prevent a worsening situation. After they finally escape the danger they faced in CAR, children and women who flee must not die from malnutrition," she said in a statement.

Between 20 and 30 percent of the refugees are suffering from acute malnutrition, well above what is internationally recognised as an emergency threshold of 15 percent, the United Nations said.