Heathrow Airport officials say a ”serious accident” has taken place involving two vehicles on the airfield at Terminal 5.
In a statement, the airport said it was “working closely with the emergency services and updates will follow”.
At least one plane is understood to have returned to its gate and passengers were removed.
The crash involved two airside vehicles.
“The airfield remains open and we will work to minimise disruption to our passengers’ journeys”, a Heathrow spokeswoman said.
The London Ambulance Service and Metropolitan Police confirmed they had been called.
London Fire Brigade said it had released two people who were trapped in the vehicles following the crash.
A Met spokesman said officers were called shortly after 6am after the crash on a taxiway.
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He added: “One male was treated for non-life threatening or life-changing injuries.
“Another male, aged in his 40s, has been taken to a west London hospital. We await an update as to his condition.
“There have been no arrests. The Health and Safety Executive has been informed.
“Officers from the Serious Collision Investigation Unit have been informed and are in attendance.”
Despite the airport insisting the incident would not impact journeys, a number of passengers posted to Twitter that they had suffered problems.
Alastair MacLeod tweeted: “Apparently there has been an accident on one of the runways at HeathrowAirport and many planes (including this one) are parked on the apron with unspecified delays of ‘hours’. No public news of this and no useful updates from British-Airways – anyone out there know any more?”
After Heathrow responded to say the accident was not expected to impact journeys, Steven Ross replied: “With respect, it is impacting journeys departing B gates – BA710 to Zurich delayed by +2 hrs and aircraft change required. Sending good wishes to injured staff.”
Additional reporting by agencies