BBC News at 15.08:
No-one was hurt after a man ran into the path of an aircraft
A major security alert is under way at Heathrow airport after a man with a rucksack scaled the perimeter fence and ran into the path of an aircraft.
The incident happened just after 1400 GMT on Heathrow's north runway.
The BBC's Ben Ando said eyewitnesses saw armed police officers surround the man and sniffer dogs sent in to check the rucksack.
The man is understood to have been taken into custody. No-one has been hurt in the incident.
Ben Ando said police received numerous 999 calls from members of the public.
Up to 20 emergency services vehicles were reported to have been sent to the scene.
The rucksack was recovered and explosives officers called in as a precaution.
It is understood the north runway, also identified as 27R, has been closed.
Sky News at 15.17:
A man with a rucksack has run into the path of an aircraft at Heathrow airport - sparking a major security alert.
He reportedly breached the perimeter fence at 2.30 this afternoon.
Armed personnel responded immediately and detained the man on the northern runway. They have recovered a bag.
Emergency vehicles are on the scene.
No planes have been coming in or out of the airport since the incident.
Sky correspondent Mark White said the incident comes ahead of the opening of a new terminal at Heathrow.
"Security is tight, especially with what is happening tomorrow morning with the opening of Terminal 5," he said.
"Her Majesty the Queen will be in attendance to open it and it will be a big day for BAA."
However, he said there was no connection at this stage to recent protests at the airport.
"What we know is that it was a lone man and he was carrying a rucksack, which is worrying in itself" he said.
"And he was determined to get airside."