The United Nations appealed Wednesday for $4.1 billion to provide desperately needed aid to civilians in war-ravaged Sudan and those who have fled as refugees, warning the conflict had fuelled "epic suffering".

The brutal conflict that erupted in April last year has caused a humanitarian collapse and left over half of the country's population -- around 25 million people -- in need of assistance and protection.

"Ten months of conflict have robbed the people of Sudan of nearly everything - their safety, their homes and their livelihoods," United Nations aid chief Martin Griffiths said in a statement.

The war between Sudan's army chief Abdel Fattah al-Burhan and his former deputy, Mohamed Hamdan Daglo, commander of the paramilitary Rapid Support Forces (RSF) has killed thousands, including between 10,000 and 15,000 in a single city in the western Darfur region, according to UN experts.

And the expanding fighting in Sudan has sparked rampant hunger with nearly 18 million people facing acute food insecurity.

The intense hostilities are meanwhile continuing to damage water supply networks and other critical civilian infrastructure, and left nearly three quarters of health facilities in conflict-affected states out of service.

At the same time, diseases like cholera, measles and malaria are spreading fast.

This coupled with soaring malnutrition rates has created a situation where at least one child dies every two hours in the sprawling Zamzam camp for displaced people in the western Darfur region, the Doctors Without Borders charity warned this week.

Amid widespread reports of gender-based violence, the war has also created one of the world's largest protection and displacement crises.

Nearly eight million people have fled their homes, including more than 1.5 million who have crossed into neighbouring countries, according to UN figures.

The UN and its partners said they needed $2.7 billion this year to reach 14.7 million people with desperately-needed aid inside the country.

"The generosity of donors helps us provide food and nutrition, shelter, clean water, and education for children, and to fight the scourge of gender-based violence and care for the survivors," Griffiths said.

"But last year's appeal was less than half funded. This year, we must do better and with a heightened sense of urgency."

The UN refugee agency UNHCR meanwhile said it needs another $1.4 billion to help nearly 2.7 million people -- refugees and members of their host communities -- across five of Sudan's neighbouring countries.