B.C.'s police watchdog is investigating after two people were killed in a head-on crash that shut down the Trans-Canada Highway south of Nanaimo early Monday.

The crash occurred just before 1 a.m. near the exit to the Duke Point ferry terminal.

A Nanaimo RCMP officer first saw a white GMC pick-up truck leave a home in the area of Harewood Road near 10th Street, according to the Independent Investigations Office.

The Mountie tried to stop the pickup for unknown reasons, but the driver allegedly failed to pull over and drove on to the Trans-Canada Highway.

Officers last saw the truck heading southbound in a northbound lane of the highway.

The IIO, which probes all police-involved incidents that result in death or serious harm, says officers later came upon the head-on crash between the truck and another vehicle in the northbound lane of the highway.

Alan Fraser, a driver who said he witnessed the aftermath of the crash, described the scene as looking "like a bomb went off."

Both drivers were pronounced dead at the scene.

The driver of the pickup truck has not yet been identified, but a neighbour has identified the other victim as trucker Cliff Bishop.

"Disbelief. Lots of sorrow," said Vince Johnson. "It's sombre, everybody's just shocked."

Johnson said both he and Bishop work as long-haul drivers and live next to each other in Ladysmith, just 10 minutes from where the crash occurred.

"It's crazy, the millions of miles that you run away from home and then you get taken out by something like that so close to home," he said.

In a news release, the IIO said it's investigating to determine whether police actions or inactions led to the deadly crash. It's also asking anyone with information on the crash to contact Nanaimo RCMP, which is conducting its own investigation.

"Our investigation will now determine exactly what happens from the beginning of that attempted traffic stop to the time of the collision, including whether there was a pursuit, if there was, how long did it last, was it discontinued," said IIO spokesman Ron MacDonald.

Neither the organization nor RCMP are saying why the officer attempted to pull the truck over.

"The facts surrounding the ownership of that vehicle is also part of our investigation, so we'll have more information on that in due course," said MacDonald.

The highway had reopened as of 11 a.m. Monday, according to Drive BC.