"Almost 26 million men, women and children are acutely hungry – to give you an example, that is equivalent to the entire population of Australia,” Dujarric told reporters.
"Of those 26 million, 750,000 people are just one step away from famine – which translates as IPC (Integrated Food Security) phase (classification) 5 for us.”
People in Sudan are facing a "worst-case scenario," he added.
Sudan has been mired by fighting between the army, led by Gen. Abdel Fattah al-Burhan, who is the head of the ruling Sovereign Council, and the paramilitary Rapid Support Forces (RSF) led by his former deputy Mohamed Hamdan Daglo.
At least 12,260 people have been killed and more than 33,000 injured in the conflict that started in April 2023, according to UN figures.
A humanitarian crisis continues to worsen as nearly 6.8 million people have fled their homes seeking safety in Sudan or neighboring countries.
Several cease-fire agreements brokered by Saudi Arabia and US mediators have failed to end the violence.