At least one person has been injured in the two-car collision which happened just after midday on Sunday (September 11).
According to Highways England the M4 eastbound has been closed while police investigation work is carried out.
Traffic has been released on the M4 westbound between J3 and J4, one lane remains closed.
A spokesman for the Metropolitan Police said: "At about 12.10pm there was a collision on the M4 between J3 and J4.
"Two cars are invovled.
"One person has been injured in one of the cars."
Emergency services including the London Fire Brigade, London Ambulance Service and Air Ambulance attended the scene of the crash.
Reports of traffic at a complete standstill were reported on Twitter.
It seems the traffic is causing some dangerous behaviour from motorists driving down the hard shoulder in the wrong direction, according to one Twitter post.
People travelling to Heathrow are being warned to allow extra time to get to the airport following the accident.
The Highways agency urged people to get back into their cars to allow emergency vehicles to pass.
Normal traffic conditions are expected to return this evening after 6pm.