As flames consumed the building on Thursday, authorities in Philadelphia said the blaze was likely sparked by a fire alarm.
The blaze began in the first floor of the building at 1:20 p.m. local time (2:20 a.m., EDT) and engulfed the entire building, fire officials said.
Firefighters arrived on the scene and quickly extinguished the blaze, which took nearly three hours to put out, officials said in a statement.
Firefighter Sean Baughman said the fire was a “very large fire” and took a considerable amount of time to extinguish.
“It was a very large fire that’s very difficult to control,” Baughmann said.
“They were able to put it out in a timely manner.”
As a precaution, the building is closed to the public, according to a city statement.
Philadelphia fire officials are urging anyone who may have been in the building or witnessed the fire to contact the fire department at 610-267-7100 or call 911.
The building’s owners have not yet released a statement, but officials say they are working with the city to reopen it to the general public.
A statement from the Philadelphia Fire Department said the office was being “reconstituted and re-opened” as of Monday morning.
A video posted on Twitter showed a man wearing a suit and tie walking up to a front desk and talking to a worker.
“I think you might want to make sure your stuff is all off the ground,” the man says.
The video shows the man leaving the building and walking through a corridor.
He stops in front of a door and looks down at his suit jacket, which is covered in ash.
He is seen holding the jacket up and looking at the ground, while wearing his coat.
Fire officials have not released the name of the employee who was injured.
The Associated Press contributed to this report.