A quarter of Rohingya children under the age of five who fled to Bangladesh from Myanmar suffer from potentially life-threatening levels of malnutrition, the United Nations said Friday.

The UN children's agency said that three health and nutrition surveys conducted between October 22 and November 27 showed up to 25 per cent of the young children crammed into Bangladeshi refugee camps have acute malnutrition, among other maladies.

"Nearly half the children surveyed have anaemia, up to 40 per cent have diarrhoea, and up to 60 per cent have acute respiratory infections," UNICEF spokesman Christophe Boulierac told reporters in Geneva.

More than 655,000 people from the Rohingya minority Muslim community have fled Myanmar's Rakhine state since late August during military operations that the UN has described as ethnic cleansing.

Around half of them are children.

Bangladesh's UNICEF head Edouard Beigbeder said that "our worst fears have been confirmed".

"Refugee children who have already endured unimaginable suffering in fleeing their homes are now facing a public health crisis," Beigbeder said in a statement.

On November 3, UNICEF warned that 7.5 percent of the children in one of the camps in Bangladesh's Cox's Bazar district were at risk of dying from acute malnutrition.

New surveys at the Kutupalong and Nayapara refugee camps, as well as other make-shift settlements, that included more than 1,700 children highlighted the worsening situation.

"Less than 16 per cent of children are consuming a minimal acceptable diet," UNICEF said.

UN rights chief Zeid Ra'ad Al Hussein told AFP on Monday that Myanmar clearly "planned" violent attacks on its Rohingya minority, causing a mass-exodus, and warned the crackdown could possibly amount to "genocide".