Police are appealing for information on two men seen running away from the scene of the shooting on Hindrey Road, towards the nearby Pembury Estate.
One is black, officers said, while the second is light-skinned, possibly of Asian or Turkish appearance.
Police said there was as yet no clear motive for the shootings, and no-one has been arrested.
"At this very early stage we must retain an open mind regarding the circumstances of the incident and any motive," the spokesman said.
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A 24-year-old man has been arrested on suspicion of murder after the body washed up on the Thames shoreline.
Seven people have now been arrested after a man died from serious head injuries
The 38-year-old officer was on his way home from a night shift when he collapsed. His death is not being treated as suspicious.