A father and his two school-aged sons died on Christmas Day when their house caught fire, likely due to a combination of electrical issues and a dry Christmas tree, according to Quakertown, Pennsylvania, Fire Marshal Doug Wilhelm.

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

"It is with unbearable sorrow that we share with you this Christmas morning the tragic news that the King family, in a house fire early today, lost their father [Eric] and two Richland Elementary School students," the Quakertown Community School District shared in a Facebook post Saturday.

Police and fire were dispatched to the home at 1:22 a.m. Saturday, where all five family members were asleep on the second floor of the home when the fire broke out, Wilhelm said. First responders made numerous attempts to get into the house when they arrived 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," 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 home, Wilhelm said. The mother and the family's eldest son escaped with minor burns, were treated for injuries at Lehigh Valley Hospital, and have since been released, Wilhelm said.

The coroner's office is expected to conduct an autopsy on the three bodies later next week, Bucks County Coroner Meredith Bucks said.

Two family dogs also died in the fire.

A GoFundMe page created in support of the King family has raised more than $200,000, far outpacing the initial $20,000 goal as of Saturday afternoon. (CNN: Excludes headline)