MONTREAL -- One driver shot another on Monday after a case of road rage turned violent, police said, snarling rush-hour traffic in St-Leonard as officers investigated.

The incident occurred around 1:40 p.m., when the drivers of a car and a van became engaged in an altercation on the service road beside Highway 40 near Langelier Blvd.

The driver of the car drove alongside the van, pulled out a gun and shot the van's driver in the upper body before speeding off, a Montreal police spokesperson said.

First responders rushed the victim, a 23-year-old man, to a hospital. He was conscious, and his life is not considered to be in danger, the spokesperson added.

Investigators were seeking an "important witness" who drove a white, four-doored vehicle, a spokesperson said. 

Officers cordoned off the scene, and directed traffic around the incident, closing the service road lanes in the area. 

Several businesses in the area have security cameras and investigators were hoping to gain access to the footage, the spokesperson said. 

The closures reduced traffic on the service road to a crawl on Monday afternoon, but at 4 p.m., the road reopened. Traffic steadily decreased and as of 5 p.m., it flowed smoothly in the area. 

The victim is a delivery driver from Monsieur Livre-Tout, a Saint-Jean-sur-Richelieu company.

As of Monday afternoon, the company said they had no news about their employee. 

With files from Matthew Lapierre of CTV News Montreal and the Canadian Press