Neighbors said they heard screaming Monday night and ran outside to see the wood frame home engulfed in flames. The children's mother and grandmother were frantic, yelling that the children were still inside.
Before fire officials arrived, a neighbor "punched out a window and was able to rescue at least one lady from the home," Marion County Fire Rescue spokeswoman Peveeta Persaud told The Associated Press.
She said the fire was already out of control when someone called 911 around 10:30 p.m. Monday. Rescuers were only able to access one side of the house when they arrived about eight minutes later, she said.
"When firefighters arrived on scene, flames were through the roof and had totally engulfed the home at that point. Firefighters immediately tried to rescue occupants from the burning building," Persaud said.
Authorities did not immediately identify the victims, but said a 21-year-old woman was flown to the hospital with first and second degree burns to her face and upper body.
Two sisters, ages 6 and 12, were in cardiac arrest and died at the hospital. Their three brothers, ages 15, 13 and 8, were in a different part of the 1,400-square-foot home and died at the scene.
Persaud said authorities weren't able to get to them until the blaze was extinguished.
The children's mother and grandmother were also taken to the hospital with non life-threatening injuries.
"It's never an easy things when you're dealing with fatalities especially with children involved," she said. "It is especially difficult for firefighters to deal with these situations despite all the training they undergo."
The children's mother and grandmother told authorities a space heater may have sparked the blaze, the Ocala Star-Banner reported.
Fire officials did not confirm that but said the State Fire Marshal's Office is investigating the cause.
