Emergency services are responding to an incident at Heathrow.
The airport said crews were in the multi-storey car park of Terminal 3.
Sky News understands people are being treated at the airport but their injuries are not believed to be serious.
The London Ambulance Service said a “significant incident” was declared around 8.40am.
There was a “full deployment” of resources and the ambulance service is treating it as ongoing.
A London Fire Brigade spokesperson said: “We were called at 8.14am today to assist emergency service colleagues at an incident near Terminal 3 at Heathrow Airport. Firefighters remain at the scene.”
Heathrow is advising passengers to allow extra time when travelling to the airport and to check with their airline for any queries.
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There was disruption to train and Tube services, with some delays on the Elizabeth Line and the Piccadilly Line.
National Rail said on its website that lines had been reopened allowing trains to call at Heathrow “following the emergency services dealing with an incident at the airport”.
It said: “Although lines have now reopened, disruption is expected to continue whilst services return to normal, delays of up to 10 minutes and cancellations can be expected until 11.45am.”
National Highways East said on X: “A serious incident within the @HeathrowAirport Tunnel has resulted in the closure of the #M4 spur road southbound between M4 and J4A.
“@metpoliceuk responding. We’ll keep you updated.”
It later said: “Incident has been resolved and all closures lifted on the #M4 southbound @HeathrowAirport spur road between #M4 and J4A.”
People on social media have reported vehicles were being searched at the airport.
A witness reported that “several” people had been “apprehended”.
A user on X said there was a “major backlog of cars unable to leave the vicinity or enter the drop-off zone” at Terminal 3.
In footage on X, several armed police were seen in a car park.
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