The war raging in Sudan could leave over 700,000 children severely malnourished this year, the UN said on Friday, warning tens of thousands could die unless aid was dramatically increased.

The United Nations children's agency UNICEF urged the world to stop turning a blind eye to the catastrophe sparked by the 10-month civil war.

"The consequences of the past 300 days means that more than 700,000 children are likely to suffer from the deadliest form of malnutrition this year," spokesman James Elder told reporters in Geneva.

"We won't be able to treat more than 300,000 of them without improved access and additional support," said Elder, just back from a trip to Sudan.

"Tens of thousands will likely die."

The war that broke out in April last year between Sudan's army chief Abdel Fattah al-Burhan and Mohamed Hamdan Daglo, his former deputy and commander of the paramilitary Rapid Support Forces, has already killed thousands, according to UN experts.

That includes 10,000 to 15,000 people killed in a single city in the western Darfur region,

The conflict has sparked a humanitarian disaster.

More than half the population of around 25 million need aid, of which nearly 18 million face acute food insecurity, according to UN numbers.

- 'Tip of the iceberg' -

Soaring malnutrition, coupled with the rampant spread of diseases like cholera, measles and malaria, mean children are already dying.

The Doctors Without Borders charity (MSF) said at least one child dies every two hours in the sprawling Zamzam camp for displaced people in Darfur.

The war has triggered one of the world's largest displacement crises. Nearly eight million people have fled their homes, half of them children.

"That's 13,000 children every single day for 300 days," Elder pointed out.

He said there had also been a "500-percent increase" in just one year in murders, sexual violence and recruitment of children to fight.

"That equates to terrifying numbers of children killed, raped or recruited. And these numbers are the tip of the iceberg," Elder said, reiterating the urgent need for a ceasefire, and for more aid.

The UN appealed this week for $4.1 billion to assist civilians inside Sudan and those who have fled abroad as refugees.

Of that, UNICEF requested $840 million to help reach 7.6 million of the most vulnerable children.

Elder said three-quarters of the agency's appeal last year went unfunded and urged donors to do more.

"The world needs to stop turning a blind eye," he said.

"Where is our collective humanity if we allow this situation to continue?"