Four people were killed Saturday when a crane collapsed and fell from the roof of a building onto vehicles in the street below, Seattle authorities said.

Two of the dead were crane operators and two were in cars smashed by the crane, Seattle Fire Chief Harold Scoggins said at a news conference.

The victims included three males and one female, Fire Department spokesman Lance Garland said. Three others, including a 4-month-old, were taken to a hospital for treatment of non-life-threatening injuries, Garland said.

The crane smashed six cars when it fell, according to Scoggins.

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 car was struck by the crane but survived."

Assistant police chief Eric Greening said the Seattle roadway where the collapse occurred may be closed until Sunday evening.

Washington Gov. Jay Inslee advised in a tweet that people should "stay clear of the scene and allow medical personnel and investigators to do their work."

Inslee referred to the incident as a "terrible accident" and expressed condolences to the families and friends of the victims.

The cause of the crane collapse was not immediately clear, with Mayor Durkan saying in her statement, "Determining how and why this tragedy happened will take time."