Britain began evacuating its citizens from Sudan on Tuesday, after criticism of a delay in getting its passport holders out of the restive country.
"The first flight has left and you can expect that there will be at least two more flights overnight tonight," Prime Minister Rishi Sunak's official spokesman told reporters.
Britain only announced that it had launched a large-scale evacuation on Tuesday morning, lagging other countries and 10 days since fierce urban fighting erupted, leading to hundreds of deaths.
It came after a US-brokered 72-hour ceasefire between Sudan's warring generals officially took effect.
London has faced pressure to act after unfavourable comparisons to the chaotic evacuation of Britons when the Taliban took control of Afghanistan in 2021.
British nationals trapped in Sudan on Monday said they felt "abandoned" by the UK authorities, while the furious relatives of one 80-year-old man said their father had turned down two opportunities to leave in a convoy with family members because he thought Britain would evacuate him, only for the flight to leave without him.
Sunak's spokesman said that the German military was running the evacuation site at the Wadi Seidna airfield but Britain had "the capacity to take over" if necessary.
Germany's foreign and defence ministries said earlier on Tuesday that the country planned to operate its final evacuation flight on Tuesday evening.
Downing Street said British forces were prepared to defend the airfield but would strive to avoid "active engagement" with other forces.
"It's worth emphasising that international evacuations have been taking place since Sunday and we haven't seen any significant issues... or large crowds appearing," Sunak's spokesman added.
Britain carried out a military operation Sunday to withdraw its diplomats as deadly battles raged in the Sudanese capital Khartoum.
But citing the dangers on the ground, it had held off on extracting its citizens more widely despite Western allies evacuating hundreds of their own passport holders.
The government says that some 4,000 Britons with dual nationality and 400 with UK-only passports are in Sudan, while 2,000 people have registered with the foreign ministry seeking help to get out.
The flights were prioritising the vulnerable, elderly and children, taking them on military planes from the airfield north of Khartoum.
Britons were urged only to come to the airfield if contacted.
Defence Secretary Ben Wallace said 120 British forces were involved, and a contingent of Royal Marines were in Port Sudan to "establish the safety of the area and any options".
That would allow for an increase in support if necessary, he added, raising the possibility of a seaborne evacuation via the Red Sea.
A Royal Navy frigate, HMS Lancaster, and a support ship, RFA Cardigan Bay, have both been sent to the region, said Wallace.
All UK passport holders are eligible for the flights as well as their partners, children and parents but only if those relatives have an existing right of entry to Britain, the Foreign Office said.
Pressed on other options such as Royal Navy warships, Sunak's spokesman said earlier: "We are looking at every possible option to ensure those who want to leave are able to do so."