TX – A propane leak is being blamed for an overnight explosion that shattered a rural North Texas house and burned a family of four.

Word of the leak comes from Cpl. Pam Jessel, a spokeswoman for the Johnson County Sheriff’s Office.

The explosion happened near Joshua, about 20 miles south of Fort Worth. Roger and Jonna Hopkins, both 38, and their two sons, ages 6 and 11, were burned.

Officials say a fire of unknown origin broke out in the house just before midnight. The parents had awakened the children and were leaving when the flames ignited the leaking propane.

The parents are listed in critical condition at Parkland Memorial Hospital in Dallas. Their sons’ conditions haven’t been released.