A teenager was shot in the leg as he rode his bike by another cyclist in a "horrifying" attack, police said.
The 17-year-old was attacked near the Blue Bell Lane and Glade Road junction in Huyton, Knowsley at about 18:20 GMT on Wednesday, Merseyside Police added.
He was taken to hospital with leg injuries described as serious but not life-threatening.
A 26-year-old man from Huyton has been arrested on suspicion of attempted murder and possession of a firearm.
He remains in custody for questioning.
Merseyside Police believe the shooting was a "targeted" attack and have appealed for any witnesses or CCTV footage.
Det Insp Tony O'Brien said: "Thankfully, while serious we believe [the boy] will recover from his injuries. But the consequences of firing a gun in a residential area could easily have been far worse.
"This will have been a horrifying experience for the victim, and of course deeply distressing for people who live locally."
Police said a Section 60 order, which gives officers enhanced stop and search powers, will be in place in Huyton, Knotty Ash and Page Moss until 04:00 GMT on Friday.