ST. JOSEPH, Mo. -- A fire Monday morning at a St. Joseph duplex killed four people, fire officials confirmed to KCTV5's Bonyen Lee.

The fire investigator said a space heater just inside a first floor window caused the fire that killed four people and severely injured a fifth.

Neighbors said a loud explosion woke them up around 3 a.m. Two people escaped the fire. Loved ones told KCTV5 that the victims included a 59-year-old woman, her 14-year-old granddaughter and two great grandchildren, who were only a few months old.

Firefighters said the fire was so intense that the second floor caved in. Two of the victims fell through to the first floor and two were found upstairs.

Firefighters searched the scene and found the bodies of two other people in the house later in the day. A couple believed to be the parents of the children were able to escape.

The 14-year-old's mother is recovering at Heartland East Hospital.