It's not yet clear what caused the crane to fall, Scoggins said.
Two of them were operators of the crane - which was being dismantled at the time - the others were in cars the crane crushed, Seattle TV station KOMO reported.
"A full and thorough investigation into the cause of the crane failure is being conducted by Washington State Department of Labor and Industries", the department said in a release.
While referring to the incident as "a tragic day in Seattle", Mayor Jenny Durkan said in a statement, "We also saw some miracles, including a mother and her young child whose vehicle was struck by the crane but survived". Gregg says a 28-year-old man is also being evaluated for non-life-threatening injuries at the center.
A mother and her baby were among those injured.
The city of Seattle has seen a recent rise in building construction, and tower cranes, according to the Associated Press, but Saturday marked the first crane accident in the city since 2006.
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Four people were killed when a construction crane crashed down onto cars on one of Seattle's busiest streets.
"It was terrifying", witness Esther Nelson, a biotech researcher who was working in a building nearby, told the newspaper.
"We are deeply saddened to confirm that one of our students passed away in the crane accident in Seattle on April 27".
The falling crane, which had been situated on top of a building, damaged multiple cars, the department said. 'The other half fell down on the street, crossing both lanes of traffic'. Police and the state Department of Labor and Industries were investigating, which Durkan said could take months.
The crane collapsed shortly before 4 p.m.at the construction site for a new Google campus.
The second fatality in another vehicle traveling on Mercer Street has not been identified.