At 15:35hrs on Tuesday, 30 August police were called to an address in Turnpike Lane, N8 by a mother reporting that her son had been shot.
Police, the London Ambulance Service and the London Air Ambulance were called to the scene, and the victim was rushed to hospital, believed to be suffering from a gun shot injury to the head. He remains in hospital in a critical condition.
At this early stage in the investigation it is believed that the victim was outside his home with some friends when a man fired a number of shots at the group.
He is described as of Mediterranean appearance and aged around 18. He has walked in the direction of the victim with another man, along Turnpike Lane, from the direction of Turnpike Lane tube station.
The other man is described as black and aged around 18.
After the shooting it is believed that the two men made off on bicycles along Turnpike Lane in the direction of High Street, N8.
Detective Chief Inspector Dan Brown, leading the investigation from the Trident and Area Crime Command, said:
"Turnpike Lane would have been really busy at that time of day, with traffic and people on foot. If you saw the shooting or anything that may help and have not yet spoken to police then please get in contact with us."
Detectives are investigating if the shooting is linked to an incident earlier that same day. At about 13:30hrs the victim, his brother and some friends were driving along High Street, N8 near the junction with New River Avenue when one of the occupants of the car noticed a man, on a bike, that he knew. The car stopped and two of the occupants, the victim and his brother, were involved in a row with the man.
A 20-year-old man was arrested in the early hours of Thursday, 1 September, on suspicion of attempted murder. He is in custody at a north London police station.
DCI Brown, added:
"At this stage in the investigation we are keeping an open mind regarding possible motivation, but one line of enquiry we are looking into is if the shooting is linked to this earlier row.
"The man involved in the altercation has been described as having olive skin. The row happened in the street, and I'm sure will have been witnessed by a number of people. If you were out in the High Street and saw anything that may help then please pass that information to us.
"This was a bold attack in broad daylight on the victim's doorstep and I want to hear from anyone that knows who the suspects are or who may have vital information for us."
Officers investigating the shooting on Tuesday 30th August, outside 159 Turnpike Lane have reviewed whether this incident is linked to a previous incident on Friday 26th August, where a man was shot in the foot. There is no information which suggests any link between the two incidents at this time, however both incidents continue to be investigated by Trident and area crime command.
Anyone with any information is asked to contact the police on 101, or call Crimestoppers anonymously on 0800 555 111.