Monmouth County authorities say a late-night house fire in Middletown that left a mother and daughter dead has been determined have started accidently.

An autopsy on  53-year-old Diane Young and her 27-year-old daughter Jacqueline Young has concluded the pair died of smoke inhalation Monmouth County Prosecutor's Office Charles Webster told the Star Ledger.

The fire originated on the second floor of the Ideal Avenue home according to Webster.

Police had initially treated the fire as a crime scene, putting up yellow police tape around the home.

WABC TV reports firefighters were concerned that no one was outside the home as they arrived to fight the fire.

"I knew the young lady that lived there," one neighbor told WABC TV. "She was a friendly girl. She was always walking up and down the street with her dog. Very, very friendly. It's just a shame."

The Star Ledger reports Diane and Jacqueline opened their home to neighbors who lost their power during Superstorm Sandy

The Prosecutor's Office is involved in the probe as is the Sheriff's Department.