A family of three was killed when a concrete slab from a bridge detached and fell on their passing truck in Washington state Monday morning.

The truck was crushed and the couple, in their 20's, and their baby boy were pinned by an enormous chunk of concrete that measured approximately 80 to 100 feet.

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"It was immediately clear to all the first responders that arrived on scene that it was an unsurvivable event," Bonney Lake Police Officer Todd Green said.

Bonney Lake police said a contractor was installing a sidewalk on the permanent bridge barrier on State Route 410 when the accident happened. 

A witness said the incident happened so fast.  "I could hear three snaps, and down it went on top of the truck," witness Dawn Nelson said. "There was nothing anyone could do. It was just surreal."

Earlier reports said one person had been killed. However, when police completed their clearing operations on the damaged vehicle, they found three bodies under the rubble. 

The family was not identified, but authorities said they were from the Bonney Lake area.  The infant was roughly six months old.

Investigators are still finding out how the concrete slab fell, as they probe state labor safety authorities.

The contractor was identified as WHH Nisqually Federal Services. The company did not issue any comment as of the moment, but said it was investigating the incident.

State records showed the company had no citations or violations so far since it was put up. 

Bonney Lake Mayor Neil Johnson said the sidewalk project aims to provide a safe walkway for pedestrians crossing the bridge.

TagsBonney Lake, Washigton State, State Route 410, accident