Explosions ignited by a fatal 14-vehicle pileup on Highway 400 sent fireballs into the sky and forced drivers to flee from their cars late Tuesday night.

Sgt. Kerry Schmidt, with the Ontario Provincial Police's highway safety detail, said the devastation from the collision was "beyond description" and "probably the worst" he's ever seen in his career.

At least three people were killed in the crash and ensuing blaze.

Once firefighters extinguished the fire, the stretch of highway near Cookstown was littered with the burnt-out frames of cars and trucks, including two fully-loaded fuel tankers that were completely consumed.

Earlier crash

Police said that about 40 minutes before the pileup, another three-car collision slowed traffic down to a crawl in the northbound lanes. Cars were backed up several hundred metres, according to witnesses.

Officers at the scene then heard a loud smashing sound, followed by a series of intense explosions.

(Kerry Schmidt/Twitter)

One witness told CBC Toronto that a transport truck slammed into the back of another truck, initiating the pileup.

(Kerry Schmidt/Twitter)

Firefighters from eight different local services responded to the scene.

(Tony Smyth/CBC)

(Tony Smyth/CBC)

'Absolute devastation'

Schmidt said in an interview that first responders were shocked once they laid eyes on the crash site.

(Supplied)

He struggled to find words to describe the pileup, saying it had caused "absolute devastation."

(Supplied)

(Supplied)

Emergency services were on scene Wednesday investigating what or who may be responsible.