A man has been rushed to hospital with a head injury after being attacked.
Met Police say they were called at around 8.00pm.
A crime scene remains in place on Northolt Road.
South Harrow Tube Station has also been closed at the request of the police.
Police say that one man has been arrested.
The victims condition is currently unknown.
One local resident took to Twitter saying he “Walked into a full on gang fight on my way home in South Harrow with cricket and baseball bats”.