A man has died at Heathrow, after a "serious accident" involving two vehicles on the airfield. One suffered non-life-threatening injuries, the other died after being rushed to the hospital.
They said one man was taken to the hospital with a broken shoulder.
Some flights at the airport have been delayed due to the incident, but passengers have been told to check in as normal.
A spokesman for Scotland Yard said: "Police were called at 6.06am on Wednesday, February 14, following a collision between two airport vehicles on the taxiway at Heathrow Airport".
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"It looks like some airport or airline staff may have been injured and police required an area to be closed off which prevented some planes from leaving their gates".
Airport officials say it involved two vehicles on the airfield at Terminal 5, and hundreds of passengers have reportedly been evacuated from planes.
The man, believed to be in his 40s, was taken to hospital following the crash, which led to around 20 flights being delayed from Terminal 5.
It added that the deceased man has yet to be formally identified, but his next of kin had been informed.
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A stock image of Heathrow Airport, which is just west of central London.
"We have apologised to customers for the delay to a small number of our flights this morning, following an incident involving two operational vehicles at the airport", he said.
The airfield remains open.
The Health and Safety Executive were informed of the incident, but no arrests were made.
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"This incident did not involve any passengers and is not expected to cause any impact on journeys today", it added.