Four people died Thursday after two semi-trailer trucks were involved in a head-on collision on the Trans-Canada Hwy. east of Chilliwack, B.C.

A compact car was also caught in the collision.

The deceased included the two truck drivers and two people who were travelling in the car.

The collision occurred on the Trans-Canada near Annis Road in the eastbound lanes at about 2:20 p.m.

Police say a semi truck was travelling westbound, when it crossed the median into the east bound lanes.

It collided with a small car and then the semi which tried to brake but couldn't.

The collision disrupted traffic which was diverted at Prest Road west of the accident.

After being closed for much of the day, the Trans-Canada's westbound lanes between Prest Road and Annis Road reopened at 10:00 p.m. Thursday.

Eastbound traffic was expected to be flowing again by 1:00 a.m. Friday morning.

Robert MacMullan witnessed the carnage after he heard a horrible noise from his office near Highway One and Annis Road.

"I heard a large crash and I immediately looked out on the highway and saw a large puff of smoke,'' he said.

"The smoke was very black, very heavy, very thick. Lots of flames, so I immediately jumped in my truck and ran down to see what I could do."

But there was little he could do.

Both trailers were completely engulfed and gone. The small car was completely demolished.

"This is one of the worst accidents we've seen in a while. It's very tragic," said Fraser Valley RCMP Const. Lea-Dunlop.

"All the people were dead when we arrived on the scene. They likely died instantly."

With a report by CTV British Columbia's Jon Woodward.