It comes as dozens were reported to have been killed in two blasts at Brussels’ airport and another explosion at a metro station in the capital.

In a statement the FCO said public events and busy public areas across Belgium were likely to see security beefed up.

Flights to the airport have been diverted, and the FCO said passengers due to fly should contact their airline for information about flight arrivals and departures to and from Brussels.

It has also urged British citizens to “stay away from crowded places and avoid public transport at this time”.
The Belgian Crisis Centre has given the Belgian telephone number 0032 2753 7300 for concerned family/friends or 1171 for general enquiries.

The Belgian government has placed the whole of Belgium at threat level 3 – a possible and real threat.

You should remain alert and vigilant, especially in places where there’s a high concentration of people. Those affected can find more information on the Belgian Crisis Centre website and Twitter feed.

The FCO also adds: “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.

Police operations are likely to continue in Forest and Brussels; you should follow the instructions of the local authorities.”

Abta said Belgium is a popular destination for UK visitors, although it noted that March is one of the quieter months for leisure travel.