A Castle Hill house fire was upgraded to a "second alarm" by Fire & Rescue NSW this afternoon, with fears a person could be inside.
Firefighters were called to a house in Castle Street about 12.30pm and raised the second alarm when it was reported a person reported was unaccounted for.
Crews in breathing apparatus got to work with house lines and began a search of the building which by this time was well alight in a front bedroom, with smoke filling the rest of the dwelling.
The fire was brought under control and no one was located inside but four pets were found deceased.
A police officer was treated by paramedics for smoke inhalation.
Fire investigators and police are working to establish a cause.