Ellie Smith has posted a heartbreaking plea to her young daughter, Cleo Smith, begging her to "please come home to me".
It has been more than five days now since Cleo vanished from a remote campsite in Western Australia.
The 4-year-old girl, wearing pink pyjamas, was last seen by her parents at about 1.30am on Saturday in the family's tent at the Blowholes camping grounds near Carnarvon on the state's remote northwest coast.
By the time her mother Ellie Smith and stepfather Jake Gliddon woke up at about 6.30am, she had vanished – with the tent zip leaving the entrance open.
"I miss you. I love you. Please come home to me," Smith wrote on her Instagram stories, alongside a photo of her daughter and the "missing child" poster.
In a separate post to her Instagram feed, Smith urged "anyone [who] sees anything at all" to contact the police.
"My sweet girl. Come home to me," she wrote alongside another image of her daughter.
It comes as a leading detective who investigated the abduction of British child Madeleine McCann has pointed to the most concerning detail in Cleo's disappearance.
On Wednesday a crucial and disturbing new clue came to light — that Cleo wouldn't have been tall enough to open the zip on the family tent by herself.
That means detectives are now looking closely at the possibility that she was abducted.
Investigators are still not ruling out that she may have wandered off alone — with a massive land, sea and air search across the area entering its sixth day on Thursday.
However, British Detective Dr Graham Hill, who flew to Portugal to help in the hunt for 3-year-old Madeleine back in 2007, said there is one "real complication" which suggests Cleo did not just wander off.
He said it's not the height of the zipper, but the fact that her red and grey adult-sized sleeping bag also went missing.
"I would say it's a remote chance that she's got up, wandered off and taken her sleeping bag with her. I think that's highly unlikely because there'd be some disturbance. You'd see where she dragged the sleeping bag and how far is a 4- year-old child going to get in the dark?" he told the West Australian.
Speaking to reporters on Wednesday afternoon, Inspector Jon Munday said Cleo was too short to reach the zipper on her tent on her own on the morning she went missing.
It all but rules out the theory that the little girl left the tent alone on Saturday morning hours before she was discovered missing. Cleo hasn't been seen since about 1.30am Saturday morning.
"The tent certainly has multiple entries," Inspector Munday said.
"One of the major circumstances that has given us the cause for alarm for Cleo's safety is the fact that one of those zippered entryways was opened.
"The positioning of that zipper for the flap is one of the circumstances that has caused us to have grave concerns for Cleo's safety."
Inspector Munday said police had no suspects but were looking into and speaking to registered sex offenders in the area.
"This operation is the most important operation to WA Police, if not nationally."
The revelation came as a child exploitation investigator who helped in the early phases of the search for Madeleine McCann divulged that child victims of abduction typically get killed within three to six hours of being stolen.
Dr Graham Hill, founder of Behaviour Analysis at the UK Child Exploitation Online Protection centre (CEOP), told The West on Wednesday children were typically "harmed by people that know them".
"And most children that are abducted by someone who doesn't know them, if they're going to be killed, are dead quite quickly," he told the publication.
Dr Hill added that generally speaking, parents of victims were the first people police needed to "eliminate the suspicion around" before pursuing other lines of inquiry.
"As difficult as that is when parents have a missing child, you have to do it, because statistically we know that children get hurt by people that know them. And also, you have to eliminate the suspicion around the parents before you can move on and do other lines of inquiry," he said.
Screeching car tyres investigated
Gaunt also confirmed on Wednesday investigators were looking into a camper's report that a car was heard screeching about 3am, shortly after Cleo was last seen.
The 4-year-old woke for a drink of water at 1.30am and was gone from the campsite, north of Carnavon in Western Australia, when her mum Ellie Smith got up at 6am.
Gaunt said that car screeching was one of several reports received from people in the area who noticed odd activities and noises overnight.
Without expanding further, he confirmed police were not in a position to exclusively rule the car tyre noises in or out as a crucial part of the investigation.
"It's a little bit unsubstantiated but we're not ruling it out," he said.
He said of the reports of odd sounds and activities, police had "investigated and responded to the vast majority" and had been able to explain "most of them".
Gaunt added that more resources had been deployed into investigating Cleo's possible abduction as the "forecast going forward gets worse each day".
While search and rescue operations had run parallel to a criminal investigation from the outset, Gaunt said investigators' efforts had ramped up in recent days.
"That was because the circumstances around this were quite unique. The lack of information, the terrain, the weather conditions, the location, all of things gave us far more questions than we could give answers to," he said.
Gaunt said police were not exclusively treating Cleo's disappearance as an abduction.
"To say we're treating it as an abduction is not correct. We're treating it as a search and rescue first and foremost, and that remains our mission," he said.
More resources were however being put into the investigative side of the case.
"We are putting more resources into that area, because obviously as time goes on the forecast gets worse each day."
Gaunt said that despite being several days into a broadscale search, no evidence had yet suggested Cleo had gone missing on her own volition or someone else's.
"At this stage we're not really finding much that tends to give us an impression one way or the other as to what's happened," he said.
All of the beach shacks had been thoroughly searched on the inside, outside and underneath, along with every piece of infrastructure in the surrounding area and coastline.
Some of the shacks, Gaunt said, would be revisited for additional searches.