The onslaught was the latest in Sudan's more than two-year war.
The Sudan Doctors' Network, a group of medical professionals tracking the war, says at least 14 children and 15 women were among the dead in the attack late on Friday by the RSF on the city of el-Fasher.
The attack also left 21 people wounded, including five children and seven women, the group said.
Most of the wounded suffered serious injuries, it said.
The attack targeted al-Arqam Home, a shelter for displaced families in el-Fasher, the provincial capital of North Darfur, the group said.
The shelter is located at the Omdurman Islamic University.
"This massacre represents a continuation of the scorched-earth policy practised by the Rapid Support Forces against civilians, in flagrant violation of all international norms and laws," the medical group said.
The RSF did not immediately respond to a request for comment.
Mashad Organisation, a rights group, described the attack as "one of the most atrocious massacres" since the RSF began its offensive on the city more than a year ago and said it amounted to an "act of genocide carried out before the eyes of a silent world".
El-Fasher has for months the epicentre of the fighting between the Sudanese military and the RSF.
The city is the military's last stronghold in Darfur.
The paramilitary forces, who have regularly bombed the city, imposed a total blockade in July.
The United Nations and other aid groups warn that 260,000 civilians remain trapped in the city after most of its population fled RSF attacks.
Residents of el-Fasher are also suffering from hunger and disease outbreaks, including cholera, according to the UN.
Sudan plunged into chaos when simmering tensions between the military and the RSF exploded into open fighting in April 2023 in the capital of Khartoum and elsewhere.
The fighting escalated into a full-fledged war that has killed tens of thousands of people, displaced more than 14 million people from their homes and pushed parts of the country into famine.
The devastating conflict has also been marked by atrocities including mass killings and rape, which the International Criminal Court is investigating as war crimes and crimes against humanity.
