Officers are searching for a teenager after a 26-year-old woman was punched on a busy bus in Romford.
The attack happened on a 165 bus in Brentwood Road, Romford, at 5pm on Monday.
The suspect is said to run off the bus with a friend after carrying out the assault.
He is described as white, aged in his late teens and was said to be wearing a black jacket and tracksuit trousers.
The victim was taken to an east London hospital for treatment to facial injuries.
Detectives from the Metropolitan Police’s Roads and Transport Policing Command are investigating.
There have been no arrests and inquiries continue.
Anyone with information is asked to contact police via 101 or @MetCC.
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