When rescuers arrived at the garage in downtown Boston, they saw the builder at the bottom of the collapse, Dempsey said. The worker is believed to have been in the crane when it fell about nine floors, Boston Police Chief Kelley McCormick told a news conference, noting that there was “a huge amount of debris.” “It’s a building that is being demolished, so these buildings are always dangerous,” Dempsey said. The worker will not be recovered until engineers complete an assessment of the area and determine that it is structurally safe, officials said. “We will not put anyone there until it is safe to do so,” said the fire commissioner. A passerby who saw the collapse asked to be taken to hospital, a Boston EMS official said. Their medical condition was not immediately disclosed. Boston Mayor Michelle Wu promised the collapse would be investigated. “This is a horrific tragedy and my heart goes out to the family and loved ones of the worker here tonight,” Wu said. “The city will work to do what it takes to understand what happened here.” CNN’s Andy Rose contributed to this report.