JACKSONVILLE, Fla. -- A woman was killed and three other people were injured when the roof of a burning Arlington apartment complex collapsed Tuesday afternoon.

Scores of firefighters responded to a three-alarm fire at the Chelsea Courtyards apartment complex on University Boulevard North, just south of Jacksonville University.

The fire call went out just before 1 p.m. When firefighters arrived, flames were already burning through the roof and people were dangling from second-story windows, desperate to get out of the burning building.

"They were rescuing people ... out of the windows with ladders," one witness said. "Pretty intense."

Firefighters don't yet know what caused the fire, but they believe it started in apartment 20 -- the unit where the woman's body was found. She was identified as Stephanie Karr.

A state investigator did say a preliminary investigation showed the fire could possibly have started from an electrical shortage, but said the cause is still undetermined.

Tenant Roderick Brooks said he tried to rescue the victim, but the fire was too intense.

"I opened the door; smoke's rushing in," Brooks said. "She had flames shooting out her door. It was burning me and I ran back out here."

One of those injured was a firefighter, who was overcome by smoke.

One firefighter rescued two cats by smashing a window and reaching in to get them.

Jacksonville Fire-Rescue spokesman Tom Francis said the fire caused an estimated $1 million damage. A total of 19 people were displaced by the fire. The American Red Cross was providing temporary housing and other assistance.

Many of the homeowners returned home from work late in the day only to find out they had lost everything.

"That's probably the most difficult part is as they're coming home from work they're finding out," said Christian Smith, an American Red Cross worker. "They're trying very hard to get in touch with them, but it doesn't always happen, so you will have families that have to come in and learn they've lost their home."

"Sad to lose my stuff, sad to lose that human being, because she was an older lady," said Rasul Elbey, whose apartment burned in the fire. "She's gone, and you can't replace a life."

Police halted traffic on University Boulevard due to the fire activity and did not reopen it until after 3 p.m.