The United Nations warned on Monday that 800,000 people may flee Sudan amid intensive fighting by rival military factions.

Hundreds of people have been killed and thousands wounded since disputes between the Sudanese army and the paramilitary Rapid Support Forces (RSF) erupted into conflict on April 15.

"UNHCR, with governments and partners, is preparing for the possibility that over 800,000 people may flee the fighting in Sudan for neighbouring countries," the agency's chief Filippo Grandi said in a tweet.

"We hope it doesn't come to that, but if violence doesn't stop we will see more people forced to flee Sudan seeking safety." 

Grandi's tweet came as gun battles and explosions again rocked Sudan's capital Monday despite the latest truce formally agreed between the warring parties, and amid UN warnings that the humanitarian crisis had brought the country near its "breaking point".

The chaos, now in its third week, has sparked a mass exodus to neighbouring countries, including South Sudan, Egypt, Ethiopia and Chad.

Sudan hosted 1.13 million refugees before the conflict started, including some 800,000 from South Sudan.

The fighting has also triggered a mass exodus of foreigners and international staff.