Military flights will depart from an airfield outside Khartoum and priority will be given to families with children, the elderly and people with medical conditions.

"We have started contacting nationals directly and providing routes for departure out of the country," tweeted Mr Cleverly.

People will be contacted directly and the government said people should not go to the airfield unless they are called.

"The situation remains volatile and our ability to conduct evacuations could change at short notice," said the Foreign Office.