Chiswick High Road has been closed and an air ambulance has landed on Turnham Green after a man fell from a building in the Chiswick Park office development.
The man was treated by paramedics but died at the scene shortly afterwards. He has not yet been formally identified.
Police say they were called to reports of a man having fallen from a height. It is believed that the incident took place at Building 7 at just after 11am.
Eye-witnesses reported armed officers on Turnham Green but their presence there is not believed at this stage to be significant.
No arrests have been made and enquiries continue.
A spokesperson for Chiswick Park Estate Management said: “We can confirm that a fatality occurred at Chiswick Park. The matter is being dealt with by the emergency services and we are doing everything possible to support them and those who are affected on the park.”
It is likely that traffic in the area will remain heavy for the next few hours with Chiswick High Road closed between Burlington Road and Silver Crescent.
Local bus routes are on diversion.