Dashcam video captures the moment a crane toppled over in Seattle on Saturday, leaving four people dead.
In the video (which contains adult language), witnesses in a nearby car can be heard reacting as the crane tips over and crashes to the ground.
The victims include two ironworkers and a college first-year.
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Frank Kuin, a Montreal-based journalist, was in a Seattle hotel lobby when he heard a "big bang" and felt the floor shake. He said he initially thought there had been an earthquake. Then he saw motorists leaving their cars on a nearby off ramp and running toward something.
Kuin followed them around a corner and saw a chunk of the crane lying on top of cars, including three that were crushed.
"To imagine what happened to those people who just happened to be driving by was quite shocking," said Kuin, who later took photographs of the scene from his fifth-floor hotel room.
Officials do not yet know the cause of the collapse.
Washington state labor investigators were at the scene of the collapse Sunday, trying to piece together what happened, said Tim Church, a spokesman for the Washington Department of Labor & Industries.
"It's a very detailed process," he said. "It will actually be months before we have anything regarding the cause."
Church said the agency has formally opened an investigation into four companies - general contractor GLY, Northwest Tower Crane Service Inc., Omega Rigging and Machinery Moving Inc. and Morrow Equipment Co. LLC. Church said he didn't know where the companies are based.
The tower crane was being disassembled when it fell from the building, Church said.
A stretch of Mercer Street remained closed Sunday.
Of the injured, a 28-year-old man remained hospitalized in satisfactory condition Sunday at Harborview Medical Center. A mother and her infant were released from the hospital Saturday. The fourth person was treated at the scene and released.
The deadly collapse is sure to bring scrutiny about the safety of the dozens of cranes that dot the city's skyscape. With Amazon, Google and other tech companies increasing their hiring in Seattle, the city has more cranes building office towers and apartment buildings than any other in the United States. As of January, there were about 60 construction cranes in Seattle.
On Saturday, Seattle Mayor Jenny Durkan said the city had a good track record with crane safety but that officials would conduct a review.
A line of showers moved over Seattle just about the time the crane fell, the National Weather Service said. An observation station on nearby Lake Union showed winds kicked up with gusts of up to 23 mph at 3:28 p.m., just about the time the crane fell.
The office building the crane fell from was badly damaged, with several of its windows smashed.
A Google spokesperson said in a statement Saturday that the company was saddened to learn of the accident and that they were in communication with Vulcan, the real estate firm that is managing the site and working with authorities.
A crane collapsed in the Seattle suburb of Bellevue in 2006, damaging three neighboring buildings and killing a Microsoft attorney who was sitting in his living room. The state Department of Labor and Industries cited two companies for workplace-safety violations after an investigation that found a flawed design for the crane's base.
The ABC Owned Stations contributed to this report.
Seattle crane collapse: Video captures moment crane topples over, killing 4