Drone strikes have hit a major power station in the Sudanese city of Port Sudan causing a "complete power outage", the country's electricity provider said.

Explosions and huge fires have been reported near the city's main international airport as a paramilitary force targeted the key city for the third consecutive day.

Flights have been cancelled after drones hit the international airport and a hotel near the current presidential palace, reports say.

"I see a huge cloud and fire going like all around the city... and I heard also now that they were like two more loud bangs. It looks quite apocalyptic," a journalist, Cristina Karrer, told the BBC's Newsday programme.

Thick black smoke could be seen at dawn on the skyline of the previously safe city where thousands of people fleeing the two-year civil war have sought refuge.

On Tuesday, Sudan's electricity company said it was assessing the damage on its substation, which has disrupted supply of water, health and other services.

One drone targeted the civilian section of the Port Sudan airport and another one hit the main army base in the centre of the city, witnesses told AFP news agency.

A third drone struck "a fuel depot near the southern port" in the densely populated city centre, where UN officials, diplomats, aid agencies and the Sudan's army have relocated from the capital Khartoum, AFP reported.

A major hotel located close to the residence of army chief Gen Abdel Fattah al-Burhan was also hit in the attack, the witness said.

Following the attacks, the UN has temporarily suspended aid flights to Port Sudan but regular aid operations continue, said Farhan Haq, the UN deputy spokesperson.

"None of our offices, premises or warehouses have been impacted, and we continue to carry out our regular operations," Mr Haq added.

On Tuesday, Sudan's government spokesman Khaled Al-Aiser said the military was guarding the affected fuel depots "to the fullest extent possible", adding that the "will of the Sudanese people will remain unbreakable".

The military has blamed the paramilitary Rapid Support Forces (RSF) for the drone attacks which started on Sunday. The RSF is yet to comment on the attacks.

In a statement, the African Union warned that the attack on Port Sudan represented "a dangerous escalation" in the Sudanese civil war and "a direct threat to the lives of civilians, humanitarian access and regional stability".

Prior to the attacks on Sunday, Port Sudan had avoided bombardment and was regarded as one of the safest places in the war-ravaged nation.

The paramilitary group has increasingly relied on drones to reclaim its lost territories, including Khartoum which was taken back by the army in March.

The two years of fighting between the army and the RSF has killed thousands, forced millions from their homes and created the world's worst humanitarian crisis.

Both the army and RSF have been accused of war crimes.