More than four million refugees have fled Sudan since the beginning of its civil war in 2023, UN refugee agency officials say.
The world's most "damaging displacement crisis" is now in its third year, with many survivors facing lack of shelter due to funding shortages, the UN said.
"If the conflict continues in Sudan, we expect thousands more people will continue to flee, putting regional and global stability at stake," UN refugee agency spokesperson Eujin Byun said.
Sudan, which erupted with violence in April 2023, shares borders with seven countries: Chad, South Sudan, Egypt, Eritrea, Ethiopia, Central African Republic and Libya.
Sudan's regular army has been fighting the paramilitary Rapid Support Forces as leaders vied for power.
The war has killed tens of thousands of people, displaced 13 million — nearly a quarter of Sudan's population — ravaged the country's infrastructure and caused famine in some areas.
'This is a crisis of humanity'
More than 800,000 of the refugees have arrived in Chad, where their shelter conditions are dire due to funding shortages, with only 14 per cent of funding appeals met, UNHCR's Dossou Patrice Ahouansou said.
"This is an unprecedented crisis that we are facing," he said. This is a crisis of humanity.
Many of those fleeing reported surviving terror and violence, he added, describing meeting a seven-year-old girl in Chad who was hurt in an attack on her home in Sudan's Zamzam displacement camp.
The girl's father and two brothers were killed in the attack and her leg was amputated during her escape, he said.
Her mother had been killed in an earlier attack, Mr Ahouansou said.
Other refugees told stories of armed groups taking their horses and donkeys and forcing adults to draw their own family members by cart as they fled, he said.
'Absence of exposure globally'
Britain's Foreign Secretary David Lammy said on Monday there is an "absence of exposure to this crisis globally, and across much of the Western world".
"The crisis in Sudan… is the worst humanitarian catastrophe in the world currently and it is a matter of deep, deep concern," Lammy said.
In just over a month, more than 65,000 refugees have arrived in Chad’s Wadi Fira and Ennedi Est provinces, with an average of 1,400 people crossing the border daily in recent days, according to the UN refugee agency.
"These civilians are fleeing in terror, many under fire, navigating armed checkpoints, extortion, and tight restrictions imposed by armed groups," the agency said.
Over 17 million Sudanese children are out of school, 5,000 have been kidnapped or missing and 3,000 children have died in the war which broke out between the Sudanese Armed Forces (SAF) and the rival RSF on April 15, 2023, according to Sudan's National Council for Child Welfare.
Child abuse has worsened since the outbreak of the war, with UN reports revealing children have been forcibly recruited as fighters, and cases of sexual abuse and slavery have increased.
Aid has frequently come under the crossfire in the two-year-old war between the Sudanese army and the paramilitary Rapid Support Forces, which has left more than half the population facing crisis levels of hunger.
Refugees currently receive only 5 litres of water per person per day, well below the international standard of 15 to 20 litres for basic daily needs.
As part of the Sudan Regional Refugee Response, UNHCR and partners in Chad are urgently seeking over US$550 million ($850) to respond to the life-saving needs of refugees fleeing Sudan into eastern Chad, including protection, shelter, food, water and sanitation.
ABC/wires
