Three people are dead and five others are in life-threatening condition following a multi-vehicle pileup on Highway 401 in Ajax that involved at least two tractor trailers.

The accident occurred near Salem Road at approximately 10:30 p.m. Friday.

Ontario Provincial Police said traffic had stopped or was slowing down due to construction in the area. A tractor trailer rear-ended the last vehicle stopped and caused an “extreme chain reaction” involving a number of other drivers.

“As you can imagine, when that energy and that mass of a vehicle crashes into cars that are essentially stopped or moving very slowly the damage is horrific," OPP Sgt. Kerry Schmidt told reporters at the scene. “The cars were just ripped open, like tin cans almost. It was incredible the amount of damage that was sustained.”

Police spent several hours freeing people trapped inside their vehicles.

OPP Sgt. Kerry Schmidt said a man, woman and a 12-year-old boy were those killed during the accident.

Another 16 people were injured during the pileup, Schmidt said. Five of those victims are now in critical condition.

Westbound lanes at Brock Street and the eastbound lanes at Salem Road were closed as police investigated the crash, but all lanes have since reopened.

With files from the Canadian Press