Britain launched a large-scale evacuation of its citizens from Sudan on Tuesday, joining other nations racing to get their people out of the North African country after its warring factions agreed to a 72-hour ceasefire.

Britain, which has estimated that about 4,000 of its nationals are in Sudan, said military flights would depart from an airfield outside Khartoum, and would be open to those with British passports.

British Prime Minister Rishi Sunak’s spokesperson said that by 1500 GMT one flight had left with two more expected overnight, adding that Britain had the capacity to take over the running of the airfield to allow flights to continue if needed.

“The first flight has already left with British nationals, there are more flights this evening, and we’ll have many more into tomorrow,” Sunak told broadcasters.

“We’ve issued out a general call for people that they can make their way to the airfield that will then be processed and safely evacuated.”

Cyprus’s foreign ministry said the first British civilians evacuated from Sudan had arrived on the island on Tuesday, with about 40 civilians on board a plane belonging to Britain’s Royal Air Force.

Sunak’s spokesman earlier said flights would continue for as long as possible and British nationals would be taken to Cyprus, with the government facilitating their travel on to Britain.

Cyprus, a former colony and home to two sprawling British military bases, said it had activated a humanitarian rescue mechanism following a British request and would offer reception facilities for the evacuation of third-country civilians.

Sunak said that Britain was exploring other options for evacuations, including Port Sudan.

“We can’t guarantee the long term sustainability of the airfield that we’re currently using. So we’re also exploring and standing up other alternative routes for safe exit from Sudan,” Sunak said.

British Foreign Secretary James Cleverly said the government was contacting nationals directly on routes for departure but would not be able to provide escorts to the airport.

Cleverly said he had spoken, either directly or through intermediaries, with the leaders of the warring Sudanese factions to facilitate the evacuation.

“We will continue to push for the maintenance of this ceasefire,” Cleverly told reporters in London.

Defence minister Ben Wallace said about 120 members of British armed forces were at the airfield, adding that they were ready to take over the running of the airfield from Germany, who said its last evacuation flight would be on Tuesday.

The British armed forces evacuated diplomatic staff and their family members from Sudan on Saturday and the government had come under criticism from British citizens still stuck there that they were not doing enough to help others.

Britain said it was working with its international partners on the evacuation and would also continue to look at other potential options for getting British nationals out.