Around 4,000 UK passport holders have been stranded in the east African country after heavy fighting broke out.

One RAF plane has already collected people from an airfield near Khartoum, with priority being given to families with children, the elderly and people with medical conditions.

And two more flights are expected overnight - though Britons will also have to reach the airfield themselves, negotiating checkpoints and potential outbreaks of fighting, as no escorts are being provided.

Evacuation effort begins for stranded Britons - Sudan latest

Africa minister Andrew Mitchell said all British nationals in the country who want to leave should head to the airstrip "before 8pm Khartoum time" - 7pm BST - to be processed for departure, but reiterated they would have to make it there "by their own steam".

He also appealed to people to continue to register their location with the Foreign Office, and said the government was "continuing to work up other options to assist British nationals wanting to leave Sudan, including other points of exit."

It appears to be a race against time as there are fears over whether a 72-hour ceasefire, which began late on Monday, will hold.

Foreign Secretary James Cleverly said it was "impossible for us to predict how long this opportunity will last".

Around 1,400 military personnel are believed to be involved in the UK operation.

The first Hercules left Sudan this morning, according to a flight-tracking site, and landed at RAF Akrotiri in Cyprus this afternoon.

It is understood to have been carrying an advance team, rather than people evacuated from Khartoum.

Mr Mitchell said around 200 people were working in a crisis centre in the Foreign Office "day and night", with a range of government departments "joined at the hip".

The PM visited staff earlier to thank them for their work, telling them: "Keep at it... the next 24 hours are absolutely critical.

"We can make a big push as we're already doing and you can help us get everyone who wants to come home, home."

The government has faced criticism for evacuating diplomatic staff two days before a full evacuation of British nationals began.

But Mr Sunak said he had been chairing emergency meetings on the crisis everyday since Thursday - including one his minister revealed took place at 3.15am on Saturday morning - and he was "pleased that we were actually one of the first countries to safely evacuate our diplomats and their families".

He added: "It was right that we prioritise them, because they were being specifically targeted.

"Now, the security situation on the ground in Sudan is complicated, it is volatile and we wanted to make sure we could put in place processes that are going to work for people, that are going to be safe and effective and we now have over 100 people on the ground in Sudan.

"The first flight has already left with British nationals, we'll have more flights this evening, and we'll have many more into tomorrow and that is down to the hard work of lots of people and we will keep at it."

Speaking to the Foreign Affairs committee, Mr Mitchell was also questioned as to why other countries - namely France - had already carried out evacuations of their citizens and was asked if the country was doing a better job.

"No I don't," he said. "I think everyone is going about this in their own way [and] we have a much larger number of citizens to take out."

About 4,000 UK passport holders are thought to be trapped in Sudan as rival military factions battle for control.

Hundreds of people have died since the fighting started on 15 April and the evacuation comes after days of pressure for a plan to get Britons out.

Food and fuel have soared in price, electricity and internet are cut off in much of the country and the clashes have left governments scrambling to get their citizens and diplomats out.

Mr Cleverly said contact had been made with leaders of the two factions "calling on them to allow British nationals, dual nationals and minors to be evacuated".

Sky's Alistair Bunkall - in Cyprus - saw the first flight take off from RAF Akrotiri and said many more are likely to follow considering the number of people who need evacuating.

It takes about three and a half hours to travel from the Mediterranean base to Sudan.

The Foreign Office said it is also looking at other potential "points of exit" - possibly by sea via Port Sudan, according to Bunkall.

Two ships, RFA Cardigan Bay and HMS Lancaster, are being lined up in case they are needed, said the Foreign Office.

The airborne evacuations carry obvious risks for the RAF, such as potential exposure to gunfire or even missiles, according to Sky's defence editor Deborah Haynes.

Although they shouldn't be targeted, she said there is "always the possibility of a mistake, a miscalculation or a deliberate attack given the chaos and unpredictably on the ground".

Read more:
Which countries have evacuated their citizens from Sudan?
What's happening in Sudan?

Some UK citizens have manged to escape on evacuation flights operated by other countries.

Germany, Italy, Spain and France are among those that have already rescued hundreds of people from dozens of countries on their own flights.

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However, the Foreign Office said only British passport holders would be able to get a place on the UK planes.

Britain's diplomats and their families were evacuated over the weekend in a precarious mission by elite troops that took place under the cover of darkness.

Some senior Foreign Office officials will be at the airstrip to coordinate the evacuations.

The violence in Sudan comes after rival generals fell out over a deal to incorporate the Rapid Support Forces (RSF) group into the military.

The army and RSF mounted a coup together in 2021 after long-time ruler Omar al Bashir was overthrown in a popular uprising two years earlier.

However, their relationship broke down during negotiations to integrate and form a civilian government.