Black Lives Matter protesters have chained themselves to tarmac at a road into Heathrow airport in a nationwide "shutdown".
A small group of activists have blockaded a central route into the busy terminals at the height of the summer season to draw attention to issues surrounding race.
Similar events are being called for across Manchester, Nottingham and London.
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The protesters in London unfurled a large banner with the words "This is a crisis" painted across it. Many of the protesters lay down on the tarmac with their arms chained together.
Some protesters have now been arrested "but the operation remains ongoing", a Met Police spokesperson told The Independent.
Long tailbacks of cars built up at the scene. Metropolitan Police said they were called out to the area at 08:25 on 5 August and traffic congestion was a problem.
The non-national protest movement, Black Lives Matter, has expressed its outrage at shootings of unarmed black citizens in the US in recent months.
Last month, a black carer called Charles Kinsey who was trying to protect his autistic patient was shot by a policeman in Miami, Florida - and when the policeman was asked why he had done so, he reportedly replied "I don't know".
