At least 30 people were killed and hundreds were injured after fighting erupted between rival military factions in Sudan early Saturday, The New York Times has reported, citing United Nations officials.

Sudan's military, headed by General Abdel Fattah Al-Burhan, has been clashing with the government's paramilitary Rapid Support Forces (RSF) in what seems to be a power struggle following tensions over the RSF's integration into the army.

Parts of the country, including capital city Khartoum, have been plunged into violence as the Sudanese Doctors' Union earlier said it recorded deaths at Khartoum's airport and Omdurman, as well as west of Khartoum in the cities of Nyala, El Obeid and El Fasher.

Fighting was also reported elsewhere, including in cities in the Darfur region.

At the end of a day of heavy fighting, the military launched air strikes on a base belonging to the RSF in the city of Omdurman, which adjoins the capital Khartoum, eyewitnesses told Reuters late on Saturday.

The RSF claimed to have seized the presidential palace, army chief's residence, state television station and airports in Khartoum, the northern city of Merowe, El Fasher and West Darfur state. The army rejected those assertions.

The Sudanese air force told people to stay indoors while it conducted what it called an aerial survey of RSF activity, and a holiday was declared in Khartoum state for Sunday, closing schools, banks and government offices.

Gunfire and explosions could be heard across the capital, where TV footage showed smoke rising from several districts and social media videos captured military jets flying low over the city, at least one appearing to fire a missile.

A Reuters journalist saw cannon and armored vehicles on the streets and heard heavy weapons fire near the headquarters of both the army and RSF.

Al-Burhan told Al Jazeera TV the RSF should back down: "We think if they are wise they will turn back their troops that came into Khartoum. But if it continues we will have to deploy troops into Khartoum from other areas."

The armed forces said it would not negotiate with the RSF unless the force dissolved. The army told soldiers seconded to the RSF to report to nearby army units, which could deplete RSF ranks if they obey.

The RSF leader, General Mohamed Hamdan Dagalo, better known as Hemedti, called Burhan a "criminal" and a "liar." The military and RSF, which analysts say is 100,000 strong, have been competing for power as political factions negotiate forming a transitional government after a 2021 military coup.

"We know where you are hiding and we will get to you and hand you over to justice, or you die just like any other dog," Hemedti said.

A prolonged confrontation could plunge Sudan into widespread conflict as it struggles with economic breakdown and tribal violence, derailing efforts to move towards elections.

(With input from Reuters)