A manhunt has been launched after a series of unprovoked hammer attacks on pedestrians in west London, one which left a victim with serious head injuries.
Shortly afterwards, a second victim was hit with a hammer. Officers took him to hospital but he did not suffer serious injuries, police said.
Within minutes, a third man was threatened by a man with a hammer nearby but not injured.
Later that night, a a 54-year-old man was taken to hospital with head injuries after being attacked from behind, the London Ambulance Service.
Police described his injuries as "serious".
The attacker was described as a bearded man riding a bicycle, .
Detective Inspector Elly Maggs said: “It is vital that we identify, locate and apprehend the male responsible for these unprovoked and extremely violent attacks as a matter of urgency. If you have any information that could assist this investigation, please do not hesitate to call us.”
There have been no arrests and enquiries continue.
Anyone with information is asked to call police on 101 or contact Crimestoppers anonymously on 0800 555 111.