CHARLOTTE, N.C. — Crews responded to a two-alarm fire at the Federal Aviation Administration's former watchtower at Charlotte Douglas International Airport Thursday morning, according to a post by the department.

Four construction workers were trapped from the smoke, Charlotte Fire said. They were evacuated, and the fire was quickly controlled.

Social media posts showed smoke billowing out of the mid-section of the tower about 8 a.m. It was set to be demolished as part of the airport’s billion-dollar expansion and renovation project.

No one was hurt in the fire, according to MEDIC.

The cause of the fire is under investigation, and no flights were affected, Charlotte Fire said.