An OPP officer has died in a London hospital following a gun battle that erupted after he stopped a suspect on a rural southwest Ontario road.

"His family were with him, and beyond that, we now are rallying around the family to make arrangements to truly express our appreciation to one of our heroes," OPP Commissioner Julian Fantino told reporters Monday about Const. Vu Pham, a 37-year-old father of three.

"Beyond that, it's just a very sad time for all of us," the commissioner said.

In an earlier news conference in London, Fantino said Pham had been in critical condition. He didn't offer details on the officer's injuries. However, CTV Toronto's Jim Junkin said Pham sustained severe wounds to his neck and upper body.

According to Fantino, Pham had been in the intensive care unit and personally described him as being in "very grave" condition. Pham was married and the father of three young sons: Tyler, 12, Jordan, 10 and Joshua, seven.

Pham's children and his wife, Heather, were with him when he died, Fantino said.

The Saigon-born Pham, a 15-year OPP veteran assigned to the Huron County detachment, became involved in a confrontation after stopping the suspect's vehicle at about 10:18 a.m. as a result of an unspecified "call for service." Pham was shot and became "immediately incapacitated," Fantino said.

Other officers in the vicinity responded to the scene. They located and exchanged gunfire with the suspect. No other officers were injured. Fantino didn't know how many officers were at the scene of the confrontation or how many gunshots were fired. "That's all being sorted out," he said.

Some witnesses have reported hearing at least 20 shots.

"I just saw the cop across the road and a guy laying in the ditch and they were both shooting back and forth… it was crazy," Faith Weber told CTV Toronto.

Both Pham and the suspect were airlifted to hospital.

The suspect is believed to be 70 years old, Fantino said. He offered no further information about the man.

Because a civilian was also injured in the shootout, the matter has been handed over to Ontario's Special Investigation Unit. The SIU is a government body that probes every incident in which a civilian is seriously injured while in the presence of police.

As a result, Fantino said he couldn't speak to the "intimate details" of the incident. However, OPP investigators are conducting a parallel criminal investigation into the suspect.

The shooting took place on the North Line and McKillop Township Road in the Ontario hamlet of Leadbury. The area is about a two-hour drive away from Toronto, or 224 kilometres.

Authorities are looking to speak with witnesses to the shooting. Anyone with information is asked to call the SIU at 1-800-787-8529.

Pham's death brings the number of OPP officers who have died over the force's 100-year history to 104.

Shooting incidents involving OPP officers are relatively rare. According to the OPP honour roll, four officers have been either shot or stabbed since 1989 prior to Monday's incident, with three of those officers dying.

In comparison, 15 officers have died as a result of motor vehicle accidents, with an additional officer dying of natural causes.

Ontario Premier Dalton McGuinty called Monday's shooting an "opportunity for all of us just to reflect on how much we count on these men and women every single day to go out there and put it on the line."