More than 800,000 people could flee Sudan for neighboring countries amid ongoing fighting in the country, the United Nations said Monday.

The United Nations High Commissioner for Refugees (UNHCR) said that it was now working with a planning figure of hundreds of thousands of people fleeing the violence that erupted in Sudan 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 neighboring 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."

Such planning figures do not mean the U.N. necessarily expects this number of people to flee, but that it believes it is possible and is laying plans to meet the massive needs that could arise.

Grandi's tweet, which was verified by his office, came as gunbattles and explosions again rocked Sudan's capital Monday despite the latest truce formally agreed between the warring parties, and amid U.N. warnings that the humanitarian crisis had brought the country near its "breaking point."

More than 500 people have been reported killed since fighting erupted between Sudan's army chief Abdel Fattah al-Burhan and Mohamed Hamdan Daglo, who commands the paramilitary Rapid Support Forces.

The chaos and bloodshed, now in its third week, have sparked a mass exodus to neighboring countries including Egypt, Chad and the Central African Republic.

The latest figures from UNHCR teams on the ground showed that at least 73,000 people have already arrived in those countries from Sudan, a spokesperson said, adding that the figure included both Sudanese nationals and mainly South Sudanese refugees returning home.

Sudan hosted 1.13 million refugees before the conflict started – one of the largest refugee populations in Africa – including some 800,000 from South Sudan.

The fighting has also triggered a mass exodus of foreigners and international staff, with countries the world over launching frantic evacuations by land, sea and air.

Grandi's estimate of how many people could ultimately flee the violence marked a dramatic increase from last Tuesday, when UNHCR gave a planning figure of possibly 270,000 people fleeing into neighboring Chad and South Sudan.