An armed gang of youths fired shots at a police officer and bystanders during a chase, police have said.
The group of about 10 dropped iron bars and baseball bats as they fled after being spotted by a police dog handler on Saturday night.
Shots were fired in his direction as they ran from Willesden Junction station in north-west London. The officer and three others were not hurt.
Police described the gang as black and aged between 15 and 20.
Willesden station was closed on Sunday morning while police carried out a search.