An explosion in Baltimore left at least 21 people hospitalised and two dangling on sacaffolding.
The blast rocked Baltimore Gas and Electric's offices at 2 Centre Plaza in downtown Baltimore. Authorities said the explosion was related to construction on the building's "air handling and boiler system."
The Baltimore Sun reported that the workers dangling on the scaffolding were rescued through a window.
The Baltimore Fire Department said it rescued 23 people from the building and evacuated two nearby buildings just to be safe.
The fire department said that nine people were taken to hospitals in critical condition, with one other person who was in serious condition. Two individuals declined care. The status of the other 11 individuals is unknown.
The company said the building was mostly empty due to the coronavirus and the holidays.
The city's fire chief, Niles Ford, said the department was still finishing its response, and said it was focused on making the situation "as safe as possible."
When fire crews found the workers, they were still tethered into the scaffolding.
He said the incident affected the 10th floor of the building up to the roof.
Mr Ford said the workers dangling from the scaffolding were rescued from the 10th and 11th floor windows, and described them as in "pretty decent condition."
The explosion collapsed part of the building's roof.
