The collision occurred around 6 p.m. Friday near a bus loop at a shopping mall in Abbotsford, B.C., said Kellie Kilpatrick, a spokeswoman for the Independent Investigations Office of B.C.
She said a 14-year-old boy was airlifted to hospital but died of his injuries just before midnight.
"These are devastating events to families, to the police department, to the community," she said. "We understand there were a lot of people in the area who may be impacted by what they saw. There's a lot of questions being asked."
Const. Ian MacDonald of the Abbotsford Police Department declined comment, noting the IIO was investigating the accident.
Coroner Barb McLintock said authorities have notified close family members of the boy, are working on contacting members of his extended family, and she expects to release a name to the public by Monday.
Kilpatrick said she couldn't provide any details of the male police officer but said he remained at the scene.
Independent investigators who visited the scene Friday included a team director, traffic reconstruction specialist, a primary investigator, and two or three other members, she said, noting the office also sent somebody to the hospital to meet with the family.
Kilpatrick said the off-duty officer was driving his personal vehicle and investigators talked to a witness who provided a statement.
"Our preliminary investigation shows that the officer driving was in a controlled intersection and he was travelling on the green light," she said.
"So we will be back this afternoon to see if there are additional independent civilian witnesses who can confirm the initial information we've obtained so far."
Kilpatrick said the investigators will take as much time as they need to gather evidence to present to the agency's chief civilian director.
The office investigates officer-related deaths or incidents of serious harm and determines whether an officer has committed an offence.
--by Keven Drews in Vancouver