OKLAHOMA CITY (KFOR) – Authorities are investigating a large apartment fire in northwest Oklahoma City.

Around 4:30 a.m. on Wednesday, firefighters with the Oklahoma City Fire Department were called to the Heritage House Apartments near N.W. 10th and Meridian.

When crews arrived at the scene, they found flames coming from the attic.

“Our crews made an interior attack to the second floor, attempted to get a knock-down on the fire. It kept progressing, part of it was pushed by the wind,” said Shift Commander David Shearer, with the Oklahoma City Fire Department.

Firefighters backed out of the structure and started using aerial devices to fight the blaze.

Eventually, they were able to get it under control.

Officials say one firefighter suffered a minor injury and was treated by paramedics at the scene.

In all, four units were damaged by fire and one was damaged by smoke.

So far, the cause of the fire is unknown.