Charlise Mutten, 9, was reported missing from a Mt Wilson property at about 8.20am on Friday and has reportedly been missing since Thursday.
Acting Superintendent John Nelson said Charlise is originally from Queensland and has been holidaying with her family in Mt Wilson over the school break.
Charlise is described as being of Caucasian appearance, with brown hair.
It is believed she was last seen wearing a pink top with a round neck collar, a black knee-length skirt and pink Nike thongs.
More than 100 emergency services personnel are currently looking for the girl.
Hundreds of officers, along with State Emergency Service (SES) and Rural Fire Service (RFS) crews, are looking through dense bushland at Mt Wilson.
Superintendent Nelson said Mt Wilson is a large area to search and police will use all resources possible to try and find the girl.
“The Mt Wilson area is a small community surrounded by bushland and some rugged bushland,” he said.
The search restarted at first light with police holding grave concerns for the girl’s welfare.
Crews looked in tents and bins for any sign of the child yesterday.
“A command post has been established at the Mt Wilson RFS Station with volunteers from the RFS and SES assisting police from the Blue Mountains Police Area Command, Police Rescue, the Dog Unit, and PolAir,” NSW Police said in a statement.
Police divers are also searching a pond in the Mt Wilson area.
Officers are investigating all possibilities in the search for Charlise.
“She’s a nine-year-old girl and she’s missing we’re here to pull out every stop that we can,” Superintendent Nelson said.
“We’re not discounting any scenario at this stage.”
A woman was comforted by ambulance officers at the search centre before being taken to a Katoomba hospital.
Police are appealing for help from the public and have sent out geo-targeting messages.
Her parents’ house has also been searched and is under police guard.
Superintendent Nelson said it is a “traumatic” experience for the family.
A car was seized in Penrith by police yesterday.
9News understands the homicide squad has been called in to assist local detectives.
Anyone who has seen a Charlise is urged to contact police or Crime Stoppers on 1800 333 000.