A man died after two vehicles crashed on the tarmac at Heathrow Airport this morning.
Emergency services rushed to Terminal 5 at around 6am following reports of a "serious accident" involving two members of staff.
One man, in his 40s, went into cardiac arrest on the taxiway, between the departure gates and the runway.
Medics battled to resuscitate him both at the scene and en route to a London hospital. He later died.
A second man was treated for a non-life threatening shoulder injury.
Hundreds of passengers on at least one British Airways plane were told to leave the aircraft following the incident, which has caused serious delays to at least 25 flights.
A spokesman from the Metropolitan Police said there have been no arrests.
Traveller Alastair MacLeod, who was queuing for a BA flight to Zurich when the incident happened, said: "I was boarding through B48 at around 6:40am there was a visible incident of some kind of a stand outside the window by the boarding gate.
"I spoke to the BA staff on the desk who were also curious but uninformed.
"We boarded, waited, and then the captain gave a series of apologies and further delay announcements. At around 8:55am we all deplaned and I’m now back in the terminal waiting to see what happens next."
Heathrow Airport confirmed the incident on Twitter but initially said it was not expected to cause delays.
Twitter user Steven Ross said: "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."
Heathrow Airport told Mirror Online: "We can confirm that following a serious accident involving two vehicles on our airfield, an airport colleague has passed away.
"Our deepest condolences go to the family and friends affected by this accident. We will be fully cooperating with the police in the investigation which will follow."
A team from the Health and Safety Executive attended the scene and is helping Met Police officers with their investigation.
A Metropolitan Police spokesman said: "Police are investigating following a fatal collision at Heathrow Airport.
"Police were called at 06:06am on February 14 following a collision between two airport vehicles on the taxiway at Heathrow Airport.
"Officers attended with London Ambulance Service colleagues.
"One male is believed to have sustained a broken shoulder; his injuries are not life-threatening or life-changing.
"Another male, aged in his 40s, was taken to a west London hospital with serious injuries. He has since died.
"Officers have informed next of kin. We await formal identification.
"A post-mortem will be scheduled in due course.
"There have been no arrests.
"The Health and Safety Executive has been informed.
"Officers from the Met’s Serious Collision Investigation Unit are investigating."
British Airways confirmed: "A number of stands at Terminal 5 are currently inaccessible and this is causing some delays.
"We are sorry for any inconvenience caused."
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