A major security alert has taken place at Heathrow airport as a man with a rucksack scaled the perimeter fence and ran into the path of an aircraft.

Eyewitnesses told the BBC armed police surrounded the man on the north runway.

Police said a man was arrested and a controlled explosion of a bag found nothing suspicious. They later said the incident was not terrorism-related.

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The alert, which delayed some flights, comes a day before the Queen will open Heathrow's new Terminal 5 building.

BBC correspondent Ben Ando said police had received numerous 999 calls at 1405 GMT from members of the public.

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Reports were of a man of Asian or Arab appearance removing his shoes before scaling the airport's perimeter fence, he said.

It is understood a message sent from the pilot to air traffic control alerting them to a man on the runway may have been overheard by the police, allowing them to act swiftly.

Up to 20 emergency services vehicles were reportedly sent to the scene where the rucksack was recovered and the controlled explosion was carried out.

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