According to Quakertown, Pennsylvania, Fire Marshal Doug Wilhelm, a house fire caused likely by the combination of electrical issues and a dry Christmas tree on Christmas kills a father and his two young sons. 

"The area of origin was a Christmas tree, so we're not sure if it's because electric or dried up old Christmas tree," Mr. Wilhelm told CNN on Sunday.

The Quakertown Community School District shared a heartfelt post on Facebook that said: "It Is with unbearable sorrow that we share with you this Christmas Morning the tragic news. The King family, in a house fire early today, lost their father (Eric) and two Richland Elementary School students."

The fire broke out on the house's second floor, where all five family members were asleep. Local police and the fire department were dispatched at around 1:22 in the morning, according to Mr. Wihelm. 

First responders made numerous attempts to get into the house but had a hard time getting in due to the magnitude of the blaze, the fire marshal said.

"It was too dangerous to get inside on the front side of the building with the fire," Mr. Wilhelm told CNN.

"The front door and front window were blocked; fire was advancing to the entire home at that point. It was very difficult for firefighters to make a safe entry. It took a while."

When firefighters finally entered the home, they discovered the bodies of Eric King, 41, and his two sons on the second floor of the two-and-a-half-story house.

The mother and the family's eldest son escaped with minor burns and were treated for injuries at Lehigh Valley Hospital and have since been released.

Bucks County Coroner Meredith Buch said that the coroner's office is expected to conduct an autopsy on the three bodies. 

Two family dogs also died in the fire.