Traffic is piling up at Kew Bridge in both directions following an accident involving a motorcyclist and pedestrian.
Paramedics from the London Ambulance Service (LAS) are treating one man currently at the scene.
A LAS spokeswoman said: "We were called today at 3.50pm to a road traffic collision involving a motorcyclist and a pedestrian on Kew Bridge.
"We sent one responder and an ambulance crew who are still at the scene."
Kew Bridge has been partially blocked due to the accident and motorists can expect delays in Chiswick and Kew and surrounding areas.
Congestion back to Chiswick roundabout and to Chalker's Corner.
Bus routes 65 and 391 are also subject to diversions and delays southbound.
People are advised to use alternative routes.
Tfl Traffic News tweeted: Kew Bridge S/B - single alternate lane working; southbound traffic having to use northbund carriageway.
"Seek other routes. Expect delays."
Drivers have experienced delays at Chiswick roundabout in recent weeks due to traffic light failures and are now baring the brunt of the closure of Chiswick Bridge.