Police have descended on the A322 as motorists saw officers stop and search a lorry heading toward Bracknell.
Now it has been confirmed that 21 people have been arrested at the scene for immigration offences.
Thames Valley Police are working with Surrey Police and Home Office Immigration on the incident.
Reports from the scene tell of around a dozen police cars and officers present.
A Thames Valley Police spokesperson said: "The carriageways of the A322 towards Bracknell on Bagshot Road where Bracknell Road is closed.
"Diversions are in place and would advise motorists to avoid the area at this time."
The road reopened shortly after midday.
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