Merseyside Police were called to the car park of The Netherton pub on Church Road in Litherland following reports a man had been shot as he got into a car. Officers raced to the scene shortly after 7pm.
A 33-year-old victim was taken to hospital for treatment to a gunshot wound to his torso, police said.
His condition is described as “serious”.
Merseyside Police has launched an appeal for information and officers believe the victim was targeted.
A large police cordon has been placed in surrounding areas.
A spokesman for the force said: “We are appealing for information after a man was shot in the torso in Litherland this evening.
“It was reported the offender was around 5ft 6in tall and was wearing a light grey or blue jacket. He reportedly arrived at the scene and left in a car.
“Officers have established a cordon and will remain in the area to carry out forensic, CCTV, house-to-house and witness enquiries, and to speak to the local community.
“At this stage, the shooting is believed to have been targeted.”
Merseyside Chief Inspector Rob Ross described the incident as an “incredibly reckless and dangerous act”.
He said: “The use of a firearm in a pub car park on a Saturday evening is an incredibly reckless and dangerous act, and we share the anger the community will feel at news of this attack.
“Our officers are currently speaking to witnesses and studying CCTV footage for clues as to why this happened, and most importantly who is responsible so they can be brought to justice.
“We’re keen to hear from anyone we have not yet spoken to who witnessed the incident, or saw or heard anyone acting suspiciously in the area around 7.10pm.
“You may live near the pub or have been passing the area at the time on foot or in a vehicle. Any information you have, or dashcam or CCTV footage, could help us find the person who did this and remove them from the streets.
“Through intelligence from our communities and a number of proactive policing operations and tactics, we have seen a decrease in firearms incidents over the past two years.
“We’re determined to keep preventing them from happening so that our communities can continue to live, work and enjoy going out of an evening free from the fear of such incidents.
“If you tell us anything you know about this incident, we will take positive action and make Merseyside safer.”
Anyone with information is urged to contact the force using the reference 22000003342
Alternatively, the independent charity Crimestoppers can be reached anonymously, on 0800 555 111.