Planes flying to Brussels from Heathrow Airport may be cancelled or diverted as a suspected terror attack in Belgium has caused Brussels Airport to close.
Two explosions occurred at the Belgian capital's main airport, with passengers being made to evacuate the terminal and 13 people reported dead.
Explosive devices were detonated near to the American Airlines check-in desk at around 8.10am, with a separate blast taking place at a metro station in Maalbeek one hour later.
The airport is in "lock down" with all flights cancelled and rail traffic towards the Belgian airport suspended.
It is feared that at least 20 are injured, but these reports have not been confirmed.
Eurostar services from St Pancras to Belgium have also been suspended until further notice.
In a statement, a spokesperson for Heathrow Airport said: "We take the safety and security of our passengers and colleagues very seriously.
"In the light of events in Brussels airport, we are working with the police at Heathrow who are providing a high visibility presence.
"We expect flights to Brussels Airport to be affected and ask passengers travelling there to check their flight status with their airline."
Brussels Airport's Twitter account told followers: "There have been 2 explosions at the airport. Building is being evacuated. Don't come to the airport area.
"Don't come to the airport - airport is being evacuated. Avoid the airport area. Flights have been cancelled."
This will affect planes coming in from Heathrow, with the London airport Tweeting to tell travellers to check all flight statuses with individual airlines.
A Belgian news agency is reporting that shots were fired and words in Arabic were heard being shouted before the blasts.
Sky News Middle East correspondent Alex Rossi, who was at the airport en route for Tel Aviv, told the channel: "I could feel the buildings move."
Mr Rossi told Sky News people were "dazed and shocked".
"The word is definitely two explosions.
"The thinking here by everybody is that it is some kind of terrorist attack although that hasn't been verified by anyone here at the airport.
"No word too of casualties. Don't know how the explosion took place, the method if you like. But it certainly seems Brussels airport has been targeted in a terrorist attack.
"We are all being moved out of the airport now towards the emergency exit. There is a great deal of confusion here. Certainly there are a number of very upset, as you might imagine, very frightened people."
He added: "There are fears that there might be other attackers."
Military officers have been deployed on the streets surrounding the airport.
As a result of the attack at Maalbeek metro station, all metro stations in the city has been shut down until further notice.
A spokesman for the UK Foreign Office said: "We are liaising with the local authorities and stand by to help any British nationals who may have been affected by the incident at Brussels airport."
Brussels officials have supplied the following number for those seeking information or who are worried about family and friends: (+32) 02 506 47 11.
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