An extra RAF evacuation flight for British nationals still trapped in Sudan was due to depart on Monday.
Foreign NHS staff and their dependants with the right to live in Britain were also eligible for what is being billed as the last UK airlift from Sudan.
The UK has so far carried 2,122 people on 23 flights.
People needed to reach to the airport in coastal city Port Sudan, 500 miles from capital Khartoum where previous planes took off, by noon local time.
Another flight, an RAF Atlas transport plane, was due to leave at 20:25 local time (19:25 BST).
Airstrikes and fighting have been reported over the weekend despite a ceasefire between rival army factions.
Tens of thousands of people have fled the country since fighting engulfed the country more than two weeks ago.
The capital city Khartoum has seen the heaviest fighting, with the Sudanese military and the Rapid Support Forces, a powerful paramilitary group, fighting for control of the country.
Sudan’s military said on Saturday it was launching a major new offensive against RSF positions in Khartoum.
- Inside overwhelmed Sudan port as thousands flee
- Why has fighting broken out in Sudan?
- NHS doctors told they can catch last UK evacuation flights
- Sudan crisis ‘risks becoming a nightmare for the world’
The latest truce, which has not held, was due to end at midnight on Sunday. But the RSF said the ceasefire had been extended for another three days.
The British Ambassador to Sudan is leading the UK’s regional response from Addis Ababa in neighbouring Ethiopia.
The UK government on Friday announced non-British NHS staff in Sudan could catch evacuation flights out of the country, in a U-turn on its previous policy.
Defence Secretary Ben Wallace said: “I am grateful to our armed forces who have ensured there was an alternative to Wadi Saeedna and who are currently supporting FCDO and Border Force staff to facilitate the rescue effort.”
The UK initially faced criticism for starting its evacuation after other countries, including European nations which rescued hundreds before the first British airlift took place.
A separate operation days earlier saw special forces troops evacuate UK diplomats from Khartoum after fighting broke out around the embassy.
- Foreign, Commonwealth and Development Office