Emergency serveices rushed to the scene at Boode Croft in Stockbridge Village at around 6.30pm ollowing reports that a man had been shot.
Officers arrived to find the teenage victim was suffering from a serious gunshot wound.
Paramedics provided CPR at the scene, but were unable to save the man’s life.
Police have cordoned off the surrounding area whilst forensic teams carry out examinations and house-to-house inquiries are made.
High visibility patrols have also been stepped up in the area in an effort to reassure the local community.
A Home Office post mortem will be carried out to establish the cause of death.
Merseyside Police Detective Inspector Tony O’Brien described the shooting as a “cold blooded, targeted attack”.
He urged members of the public and witnesses to come forward with any information they might have that would be able to assist them with their enquiries.
Detective Inspector O’Brien said: “The investigation is in its early stages and extensive inquiries are being carried out to establish the motive and to identify those responsible.
“This was a cold blooded, targeted attack on a residential street which has taken away the life of a young man and tonight a family are mourning their tragic loss.
“The people responsible for this attack knew exactly what they were doing and they need to be caught.
“There is no place in Merseyside for firearms, or those who use them and bring fear to our communities.
“We need members of the public to come forward with information so we can keep our streets safe.
“I would urge anyone who saw anything, or who has any information, which could help us with our enquiries to contact us urgently.
“You may not think that the information you have is significant but it could help us with our enquiries.”
Police in Knowsley wrote in a tweet: “A family is in mourning this evening following the fatal shooting of a 19-year-old man.
“If you have any information which could help us find those responsible please call Crimestoppers anonymously on 0800 555 111.”
This is a breaking story. More to follow…