"Parts of war-ravaged Sudan are at a high risk of slipping into catastrophic hunger conditions by next year's lean season," the WFP said in a statement.
It said this could happen if the UN agency is unable to expand access and deliver regular food assistance to people trapped in conflict hotspots including the capital Khartoum.
On April 15, army chief Abdel Fattah al-Burhan and his former deputy Mohamed Hamdan Daglo, who commands the paramilitary Rapid Support Forces (RSF), turned their guns on each other.
Two years after the former allies jointly engineered a 2021 coup that derailed a fragile democratic transition, their power struggle has killed more than 12,190 people, according to a conservative estimate by the Armed Conflict Location & Event Data Project.
The United Nations has recorded seven million people displaced across Sudan, which, combined with the lack of good harvests, means hunger stalks large parts of the African country.
The vast Darfur region in the west and Kordofan in the south, as well as the capital Khartoum, where the conflict first erupted, are at risk.
"Nearly 18 million people across Sudan are facing acute hunger ... more than double the number at the same time a year ago," the WFP said on Wednesday.
A new food analysis for Sudan, "once described as East Africa's future breadbasket", the statement said, "shows the highest levels of hunger ever recorded during the harvest season (October through February), typically a period where more food is available".
On Sunday, the head of the UN's humanitarian response in Sudan told AFP the world body had been able to reach only a fraction of the nearly 25 million people needing aid.
But assistance to even those four million could soon stop if the chronic lack of funding continues, Clementine Nkweta-Salami said in an interview.
WFP Country Director and Representative in Sudan Eddie Rowe said on Wednesday it was urgently calling "on all parties to the conflict for a humanitarian pause and unfettered access to avert a hunger catastrophe".
However, getting the warring parties to negotiate remains difficult, and both sides have been blamed for breaking truces agreed in the past.
And on December 1, at the request of the Sudanese authorities, the UN Security Council ended the world body's political mission in the country.
The United Nations Integrated Transition Assistance Mission in Sudan was put in place in 2020 to help support a move to democracy following the fall the previous year of veteran Islamist autocrat Omar al-Bashir.
