Two construction workers are missing after a massive five-alarm blaze broke out in Charlotte, North Carolina on Thursday, according to officials.

“With the extensive structural damage, the search process can be lengthy,” the Charlotte Fire Department said in a statement on their official Twitter account. “We can not confirm a loss of life.”

The Charlotte Fire Department received calls about a fire at an apartment building under construction on the 7700 block Liberty Row Drive at around 9 a.m.

Firefighters arrived within minutes to find heavy smoke conditions coming from the construction site. At 9:10 a.m., the fire became a two-alarm, and progressed to five-alarm by 9:56 a.m., Fire Chief Reginald Johnson said at a news conference Thursday afternoon.