A mom and her six children, ages 3 to 11, were killed when their Pennsylvania home exploded, leaving it engulfed in flames too severe for rescuers to be able to get inside to reach them.

The cause of the deadly blast and inferno Sunday morning remains under investigation, but police say a propane leak inside the home could have been responsible for the tragedy.

Firefighters who rushed to the residence in Lamar Township around 8:30 a.m. confirmed that seven people were trapped inside when they arrived, but that the fire was so severe they couldn’t get inside.

All seven trapped inside died, said police, who identified the victims as Sarah Stolzfus, 34; her four sons ages 11, 10, 5 and 3; and two daughters, 8 and 6.

Neighbor Christina Duck, who was eating breakfast at the time of the explosion, told WNEP-TV the concussive boom was so powerful she could feel it from inside her own home.

“And I heard a boom and I could feel it and I got up and looked out the window and I could see the flames through the windows and I come running outside and within a minute the whole house was completely engulfed,” Duck told the outlet.

Duck said her family has only lived in the neighborhood for a few months, and that she regularly saw Stolzfus’ kids playing in their yard.

Cops said exterior propane tanks located outside the destroyed home did not explode and didn’t contribute to the disaster.