A traffic collision and shots fired were reported about 12:30 p.m. at Manchester and the 110 Freeway, the LAPD said.
The CHP said a driver called to report they were injured, and a car window was broken or shot out. The caller was pulled over on the shoulder and was then hospitalized in unknown condition.
The LAPD said the victim is a 40-year-old black man. He was in critical condition and was in surgery Tuesday afternoon.
The victim was merging off the northbound 110 near Florence when another car pulled up and opened fire, according to the LAPD.
The victim pulled off the exit and crashed into a fence. A woman and another man were in the car but were not hurt.
The suspect vehicle was only described as dark in color.
The LAPD said the shooting was believed to be gang-related based on interviews.
Northbound lanes were closed while investigators walked the roadway looking for evidence. All northbound off-ramps were also closed.
Northbound freeway lanes were reopened by 2:05 p.m. The Florence Avenue exit remained closed during the shooting investigation by the LAPD.