One person was seriously injured when a massive fire tore through a vacant warehouse in Humboldt Park early Friday, a structure the city has been inspecting and securing for some time.

Fire crews responded a little after 4 a.m. to the blaze at Grand and Homan, according to the Chicago Fire Department. A third alarm was called to bring more firefighters, who were forced to take a defensive approach to the fire when the roof collapsed.

A man with a leg injury was taken in serious condition to Stroger Hospital, according to Fire Media.

The blaze was extinguished about 6:10 a.m. and the cause is under investigation.

City Department of Buildings personnel spent much of the day at the site to “evaluate the structural safety,” according to spokeswoman Mimi Simon. “Once the assessment is complete, the city will determine if the building can be saved.”

The department’s top priority is “to save buildings wherever possible, and we have been actively working for the past year to find a new use for the building,” Simon said.

The city’s Department of Law had planned to file a motion Friday morning to assign ownership to the Cook County Land Bank, which would transfer it to an interested developer.

City inspectors have been “regularly monitoring this building, and we immediately board-up and secure when we find the building open – at the cost of approximately $10,000 to date,” Simon said.