Four people were killed over the weekend when a crane fell from a building at the Google campus in Seattle during a storm.

NBC News reports that the crane fell onto six cars at the intersection of Fairview Avenue and Mercer Street just before 3:30 p.m on Saturday. Fire Department spokesman Lance Garland revealed that two of the dead were ironworkers inside the crane when it collapsed while the two others killed were inside cars which were crushed. Three others were taken to a local hospital for treatment of non-life threatening injuries.

Officials from Seattle have yet to determine the cause of the collapse but it has been confirmed that police and the state Department of Labor and Industries are investigating the incident. However, it could take months before the investigation is completed.

Business manager for the International Union of Operating Engineers Local 302, Daren Konopaski, told USA Today that the crane was reportedly being dismantled when high winds caused it to collapse.

“We don’t know, but that’s what seems to have happened here. We are in the process of trying to get information,” he said.

Seattle Mayor Jenny Durkan said that the crane collapse represented a “horrible day” for Seattle but said it was a miracle that more weren’t killed.

“It’s a horrible day in Seattle when something like this happens. But it’s a time when we come together because Seattle is a city that rallies around each other,” she said.

Seattle has more cranes on office towers and apartment towers than any other city in the United States.