The Foreign and Commonwealth Office (FCO) urged British visitors to Belgium to “remain vigilant and follow the instructions of the Belgian authorities” following the explosions at Zaventem International Airport and Maalbeek station.
Travel advice on the FCO website states: “The Belgian threat level is Level 4 – a serious and imminent threat.
“You should remain alert and vigilant, stay away from crowded places, and follow the instructions of the Belgian authorities.
“There have been a number of police raids and arrests in the Brussels region and other Belgian cities in recent weeks.
“Belgian security operations are likely to be carried out at short notice. If you’re in an affected area you should follow the instructions of the Belgian security authorities.
“Police have asked the public not to comment on police operations on social media.”
Anyone who is concerned about family or friends in Brussels can contact the FCO's helpline on 020 7008 0000.