The fire broke out on Christmas morning.

A father and his two sons have tragically died after a Christmas Day fire. It is believed their Christmas tree caught fire at their home in Pennsylvania. 41-year-old Eric King, 11-year-Liam and 8-year-old Patrick passed away on Saturday morning. Their two dogs were also lost in the blaze. Mother Kristin and 13-year-old son Brady survived the fire. They escaped with minor burns and were treated in hospital. Fire marshal Doug Wilhelm said the fire broke out around 1.30 am on Christmas morning. The family were sleeping on the second floor of the house when the blaze started. Quakertown Police Chief Scott McElree said a full investigation has now been launched. He told reporters, "We will be continuing to investigate to find out why it ignited, but the evidence is very clear that it started in the Christmas tree." [caption id="attachment_404079" align="aligncenter" width="1050"] CBS[/caption] "It was such a hot fire that most of the content where it started is burnt." “A Christmas tree burns very quickly and very hot," he explained. Firefighters struggled to get into the house because of the magnitude of the blaze. Fire marshal Wilhelm told CNN: "It was too dangerous to get inside on the front side of the building with the fire. "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." The fire spread to their neighbours home but luckily the family next door was saved because of a fire wall between the two homes. A mum, her son and their dog lived next door, but were able to escape without being harmed. Over $600,000 has been raised by the Quakertown community to support Kristin and her son Brady.