The flames broke out just before 11:30 p.m. at a home in the 3900 block of Highland Avenue in Myersville.
Fire officials say two female children, ages three and six, died in the fire.
Responding units arrived at the scene and had found the home fully engulfed in flames. Crews said they worked aggressively to locate two people who were reported to be inside the home, but their efforts were hampered by the intense fire and unstable structure.
Fire officials say the two young girls were taken to the Office of the Chief Medical Examiner in Baltimore where autopsies will be conducted on Friday. A fire investigator will be attending the autopsies.
Firefighters say six people in total were inside the home at the time of the blaze. Four people were taken to nearby hospitals. A male, age 39, was flown to Med Star Washington Hospital Center, and 8-year old female was taken to Children's National Medical Center, and a female, age 33, and a 7-month old infant were taken to Frederick Memorial Hospital.
The extent of their injuries has not been released.
Fire officials say the names of the victims will not be released until all family members have been notified.
A volunteer firefighter from Middletown Volunteer Fire Co. was also taken to Frederick Memorial Hospital for treatment.
The cause of the fire is still under investigation.