A massive crash on a Washington highway involving 23 vehicles – including three from Canada - sent six people to the hospital Saturday.

The accident took place at 8:30 a.m. near Mount Vernon on Interstate 5 highway, northbound of exit 224. Earlier in the day, two people were killed in an unrelated drive-by shooting on I-5 just south of the crash.

Images from the scene show debris littering the highway, and smashed cars strewn across the road.

Washington State Patrol Trooper Mark Francis told CTV Vancouver that a semi-truck carrying 80,000 pounds of gravel crossed the median and began the massive pileup.

The driver of the semi-truck likely experienced a medical problem that caused him to lose control of the truck, Francis says.

The driver was airlifted to Seattle’s Harborview Medical Center with a severely broken arm and “chest injuries”. His identity has not been released.

Six people in total were injured in the crash, and two individuals – including the driver of the semi-truck – were airlifted to Harbourview in critical condition.

Francis says three Canadian vehicles were involved in the smash: an SUV with Alberta plates, as well as a commercial semi-trailer and a Toyota Corolla with B.C. plates.

No Canadians were injured, although all three vehicles sustained minor damage. Francis says a family returning home from a soccer tournament was in the B.C. car.

Northbound traffic was completely blocked for hours, and was backed up for more than eight miles.

With files from CTV Vancouver’s Tom Popyk