Houses have been burned in the Sudanese capital after heavy fighting between the army and the fighting forces.
Videos posted online on Sunday showed the Greater Nile Oil Company tower engulfed in flames.
“This is really painful,” Tagreed Abdin, the architect, said in a post on X, formerly known as Twitter.
Airstrikes and ground battles have continued in Khartoum and other towns and cities since fighting began in April.
More than one million people have been forced to flee the country, the UN has said.
Located near the Nile River, the 18-meter oil refinery is one of the most recognizable landmarks in Khartoum.
Ms Abdin said she described the city’s skyline, and lamented “such merciless destruction”.
It is not yet clear what caused the cone structure of the building, which has a glass facade, to catch fire. There were no reports of injuries or deaths.
The violence in Sudan began on 15 April, sparked by a power struggle between leaders of the Sudanese army and the Rapid Support Forces (RSF).
It followed days of tension as members of the RSF were relocated across the country in a move seen by the military as a threat.
Sudan War Monitor, which provides an analysis of the conflict, said the RSF had attacked areas controlled by the military on Saturday, including an office block at the justice center. Many government buildings were reportedly burnt due to the attack.
Attacks on military bases continued until Sunday, witnesses told AFP news agency.
Residents in the southern part of the city – where the army is targeting RSF bases – told AFP they heard “big bangs” as they woke up.
Health authorities announced on Sunday that all primary hospitals in Khartoum – and the Darfur region – were out of order.
Nawal Mohammed, 44, who lives less than 3km (1.8 miles) from the clashes in the capital, said the doors and windows of his family home shook with the force of the blasts.
He described the fighting on Saturday and Sunday as “the most violent since the war began”.
According to a group of democracy lawyers, the fighting has killed “dozens of civilians” in Khartoum since Friday.
Clashes were also reported in the town of El-Obeid, about 400km (250 miles) south of the city.
The RSF has been fighting to take control of the capital, and military airstrikes have been aimed at reducing RSF positions.
The conflict has killed 7,500 people and displaced more than five million.
