Gun battles and explosions again rocked Sudan's capital Monday despite the latest truce formally agreed between the warring parties as the United Nations warned the humanitarian crisis had brought the country near its "breaking point".

The chaos and bloodshed, now in their third week, have sparked a mass exodus of tens of thousands of Sudanese to neighbouring countries including Egypt, Chad and Central African Republic.

More than 500 people have been reported killed since fighting erupted on April 15 between Sudan's army chief Abdel Fattah al-Burhan and Mohamed Hamdan Daglo, who commands the paramilitary Rapid Support Forces. 

Millions of Sudanese around the capital and beyond have sheltered in their homes with dwindling food and water and frequent power cuts, as fighter jets thundering through the sky on bombing raids have drawn heavy anti-aircraft fire. 

"Warplanes are flying over southern Khartoum and anti-aircraft guns are firing at them," said one resident, while another witness told AFP he was also hearing "loud gunfire". 

Sudanese refugees from the Tandelti area who crossed into Chad, in Koufroun, near Echbara, are seen on April 30. Photo: AFP

Burhan and Daglo have agreed multiple, poorly observed ceasefires and extended the latest by 72 hours late on Sunday, with each side repeatedly blaming the other for the frequent violations.

While foreign nations have evacuated thousands of their citizens by air, road and sea, some 50,000 Sudanese have fled overland to neighbours, said the UN. 

In a dusty makeshift camp near Adre on the Chad border, UN refugee agency staff were handing out emergency food rations to families who fled the violence with few belongings, sitting in the sand in the shade of trees.

"Today I have no food for my children and no means of work," one refugee, Mahamat Hassan Hamad, a tailor, told AFP. "My sewing machines were taken by the attackers."

'Lives turned upside down'

Sudan's turmoil has seen aid workers killed, hospitals bombed, humanitarian facilities looted, and foreign aid groups forced to suspend most of their operations.

"The scale and speed of what is unfolding is unprecedented in Sudan," said Stephane Dujarric, spokesman for UN chief Antonio Guterres. "We are extremely concerned by the immediate as well as long-term impact on all people in Sudan, and the broader region."

Top UN humanitarian official Martin Griffiths was heading to the region to help bring relief to the millions "whose lives have turned upside down overnight". 

"The humanitarian situation is reaching breaking point," Dujarric said.

People walk on a deserted street in Khartoum on April 30, 2023, as clashes continue in war-torn Sudan. Photo: AFP

At least 528 people have been killed and almost 4,600 wounded in the violence, according to Sudan's health ministry, but the real death toll is feared to be far higher. 

Fighting has spread across Sudan, including to the long-troubled Darfur region.

The UN said at least 96 people were reported killed in El Geneina, West Darfur, where supplies were seen strewn across the floors of badly damaged hospitals.

Daglo's RSF emerged from the notorious Janjaweed that was unleashed in a scorched-earth campaign in Darfur from 2003 by former strongman Omar al-Bashir, who faces charges of war crimes and genocide.

The RSF include fighters who have seen battle in Yemen where they were sent to back a Saudi-led campaign supporting the government against Huthi rebels.

Further complicating Sudan's battlefield situation, Central Reserve Police were being deployed on the side of the army across Khartoum to "protect citizens' properties" from looting.

The US Treasury Department last year sanctioned the Central Reserve for "serious human rights abuses" related to "excessive force" against pro-democracy protests after the 2021 coup that brought Burhan and Daglo to power.

UN facilities looted

The UN has warned the unrest could plunge millions more into hunger in a country where 16 million people already needed aid to stave off famine.

Only 16 percent of Khartoum's health facilities are functioning, says the UN World Health Organisation.

The fighting was pushing Sudan's already ailing health sector toward "disaster", warned the WHO's regional director for the eastern Mediterranean, Ahmed al-Mandhari.

He warned of the growing threat of cholera, malaria and other diseases as the rainy season nears and safe water supplies are becoming scarce.

A first Red Cross plane on Sunday took eight tonnes of medical supplies from Jordan to Port Sudan, which has served as an evacuation hub. 

The UN World Food Programme has resumed activities in Sudan after over two weeks of suspension following the deaths of three of its aid workers.

Regional powers have joined negotiations to help end the violence.

An envoy of Burhan's met on Sunday in Riyadh with Saudi Foreign Minister Prince Faisal bin Farhan, who called for the restoration of calm in Sudan.

Egypt, in an Arab League emergency meeting in Cairo, proposed a draft resolution Monday that called for an "immediate and comprehensive cessation" of fighting.