Residents told AFP they could hear street battles in northern Khartoum, as well as artillery fire in the south of the capital of over five million people which has been turned into a deadly war zone.
Since the truce began a week ago, frightened residents have ventured out to try and get food or water, the costs of which have doubled since the start of the war.
But thousands of families continue to shelter in place, rationing water and electricity while trying desperately to avoid stray gunfire.
In Darfur, on the western border with Chad, continued fighting "blatantly disregards ceasefire commitments", according to Toby Harward, of the United Nations refugee agency.
"Intermittent fighting between Sudanese armed forces and Rapid Support Forces in El Fasher, North Darfur over the last few days" has seen civilians killed, homes looted and tens of thousands newly displaced in the already war-ravaged region, Harward said.
Newborns dead in hospital
The persistent fighting has impeded the delivery of essential humanitarian aid, upon which 25 million people -- over half the population -- now rely to survive, according to the UN.
A week ago, representatives of army chief Abdel Fattah al-Burhan and his former deputy Mohamed Hamdan Daglo, who commands the paramilitary RSF, pledged to pause the incessant air strikes, artillery fire and street battles in order to allow in much-needed aid and civilians to flee.
But by the seventh day of the truce -- due to expire at 9:45 pm (1945 GMT) on Monday -- no humanitarian corridors had been secured, and aid had only trickled in to replenish the few hospitals that are still functioning in the capital.
In East Darfur state, more than 30 infants have died in a single hospital since fighting began, including "six newborn babies who reportedly died in one week alone due to problems including lack of oxygen amid electricity blackouts", according to the World Health Organisation.
Since April 15, at least 1,800 people have been killed, with more than a million others displaced within Sudan and nearly 350,000 fleeing to other countries.
Sudan's neighbouring states -- many already facing economic crises or mired in instability -- fear regional spillover and have pleaded for aid from the UN, itself reporting severe financing gaps.
The UN sounded the alarm again Monday, saying Sudan has become one of the highest alert areas for food insecurity, requiring "urgent" action from the international community.
Aid agencies have also warned that with the rainy season approaching in June, parts of the country will become inaccessible, while the risk of cholera, malaria and water-born diseases will rise.
Sudan's already fragile health sector faces compounded challenges, with three quarters of hospitals in combat zones out of service, according to the doctors' union.
Even health facilities in areas largely untouched by fighting and looting are unable to replenish supplies as they scramble to serve an influx of those displaced by the war.
Both the army and the RSF have said they are willing to discuss extending the ceasefire, which US and Saudi mediators called for.
But Riyadh and Washington warn that "both parties are posturing for further escalation".
The governor of Darfur -- a former rebel leader allied with the military -- on Sunday called on civilians to take up arms.
This came after calls from the army for reservists and pensioners to arm themselves, while tribes in the country's east earlier demanded to be given weapons.
The Umma party, one of Sudan's main civilian groups, cautioned "against calls to arm citizens under the pretext of protecting themselves", which it said were "attempts to drag the country into civil war".
Even with a potential extension of the truce, the UN warned there is a new latent danger amid "growing reports of unexploded ordinances" in the capital and other densely-populated areas.