Thousands of passengers face disruption after flights between the UK and Brussels were cancelled for a second day following bomb attacks in the Belgian capital.
All flights at the city's main airport, Zaventem, were suspended after two explosions in the departures hall.
The airport has confirmed that it will remain closed on Wednesday.
Eurostar was also hit by disruptions as a result of the bombings, with all services from London terminating in Lille, France.
It confirmed that two trains from London to Brussels would run "for those whose travel is a necessity", with full service expected to resume tomorrow.
Armed police were stationed at UK airports, ports, international train stations and underground stations as a precaution.
British Airways said customers due to travel to Brussels up to and including March 29 can alter their booking.
Brussels Airlines, which serves a number of UK airports, also cancelled its services from Brussels for the next two days.
The Foreign and Commonwealth Office (FCO) updated its travel advice for Britons in Brussels, urging them to "stay away from crowded places and avoid public transport at this time".
British officials in the city have been given the same instructions, the FCO said.
Anyone who is concerned about family or friends in Brussels can contact the FCO's helpline on 0207 008 0000.