Heathrow Terminal 4 has been evacuated according to reports on social media.
People took to Twitter to state the terminal was being evacuated with one user reporting that a man was arrested, while another said a fire alarm was going off.
We have contacted Heathrow to try to find an official explanation for the disruption.
Heathrow has posted a statement on Twitter to people affected apologising for the incident:
They said: "We are sorry for any inconvenience caused. We can assure you that the relevant teams are working on getting you back inside as quickly as possible."
Pictures posted on social media show hundreds of people outside the airport and a fire engine at the scene.
Follow all the updates on our live blog below:
Dutch airspace closed
Flights to Amsterdam and other destinations in the Netherlands are delayed due to a “major air traffic control (ATC) technical fault”, according to a statement.
The statement reads:
Due to a major ATC technical failure, Dutch airspace was closed around noon today and this has already affected Amsterdam Schiphol arrivals and departures. The airport tweeted in the last hour advising that there were no arrivals and departures possible. This was followed 10 minutes later by another tweet advising that departures had resumed slowly and a limited amount of flights had been allowed to land.
This is going to have a knock on effect for the remainder of the day and is likely to lead to delays and cancellations. If you are travelling today please check with your dedicated travel consultant or the airport/airline website for the most up to date information.
Picture of airport
This picture of people waiting outside the terminal was shared this morning on social media.
'Man detained under Mental Health Act'
A spokesman for the Metropolitan Police Service has told Surrey Live:
There was a partial evacuation of part of terminal 4 due to a fire alarm.
A man has been detained under the Mental Health Act after we were called to a concern for his welfare at 10.25am.
The Heathrow spokesman continued:
The individual that pulled the alarm has been arrested.
'Fire alarm evacuation'
A spokesman for Heathrow has told Surrey Live:
There was a fire alarm evacuation at T4 landside check- in, a brief evacuation followed.
The terminal is now back up and running.
Heathrow has responded to someone on Twitter, writing: “We are sorry for any inconvenience caused. We can assure you that the relevant teams are working on getting you back inside as quickly as possible. Thank you.”
A video posted on social media appears to show a fire engine outside the airport.
We have contacted Heathrow Airport to ask them for a statement on this incident and will let you know as soon as we get a response.
Good morning, there have been reports that Terminal 4 at Heathrow was evacuated this morning - stick with us for live updates on this situation.