Officers and paramedics were called to West Road in Erith at roughly 10.25pm on Monday, to reports a man had been struck by a bus.
The man was pronounced dead at the scene.
Work is ongoing to identify him, Scotland Yard says.
“At this early stage officers are investigating reports that the man was involved in an altercation immediately prior to being struck by the bus,” a Scotland Yard spokesperson said on Tuesday.
“Enquiries into the circumstances continue.”
A post-mortem examination will be scheduled in due course.
Anyone with information is asked to call police on 101 or tweet @MetCC and quote CAD 8016/28Aug. You can also provide information anonymously to the independent charity Crimestoppers on 0800 555 111.