The A312 is closed northbound at the junction of Ossie Garvin Roundabout following what police are calling a "serious collision".
Posting on Twitter at 8.33pm on Thursday (May 25), Hillingdon Police advised motorists to avoid the area.
The Tweet read: "Serious collision on the northbound carriageway of the A312.
"Road closures in place, please avoid where possible. #HERT3"
According to Transport for London, traffic is being diverted.
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As we bring our blog to a close, the A312 northbound remains closed at the junction of Ossie Garvin Roundabout in Hillingdon.
Four cars were involved in the collision, and there have been two arrests for driving offences.
Two arrested for driving offences
'Use other routes'
One their website, Transport for London write: “Traffic is slow on approach with tailbacks to Bulls Bridge Roundabout.
“Expect delays and use other routes”