OKLAHOMA CITY, Okla. (KFOR) – Fire investigators are determining the cause of a mysterious apartment fire in Northwest Oklahoma City Tuesday afternoon.

Almost 30 firefighters took down the flames at Putnam Green Apartments at 7525 Knight Lake Dr. near Wilshire Blvd. and Lyrewood Lane.

“When our fire crews arrived on scene, they were met with heavy smoke and fire in the attic,” said OKC Fire Department Spokesman John Chenoweth.

He said all eight units of the building took heavy damage, but no one lives in them since they’re being remodeled.

“It definitely could have been worse,” Chenowith said. “All these units could have been lived in. We could have had several more life hazards that were involved.”

Some witnesses told KFOR they saw a couple of people running from the building after it erupted in flames, wondering if the fire could have been started by squatters.

“We got a million of them,” said tenant Tiarra Williams. “A bunch of squatters in every building. You get rid of them in one building, they find another building.”

At the end of the day, tenants aren’t sure what happened.

“Anything can start a fire when it’s like wires connected wrong, something can be put inside the building wrong to where it can start a fire,” said Jazznay Carter. “So until the investigation is done, we won’t know anything.”

They’re also grateful no one was hurt.

“It looks horrible,” Williams said of the damage. “I’m just really glad that nobody lived there, and nobody is coming home to nothing.”

OKC Fire is investigating the cause of the fire.

Meanwhile, a representative of Putnam Green Apartments said they’ll begin assessing the cost of damages immediately.