Detectives have not given up hope of finding Cleo alive but admit all signs point to her having been abducted from the popular Blowholes campsite on WA's northwest coast six days ago.

A land search in the immediate vicinity of the campsite, north of Carnarvon, will wind down on Friday with the focus to shift to a criminal investigation.

"Given the information now that we've gleaned from the scene, the fact that the search has gone on for this period of time and we haven't been able to locate her ... it leads us to believe that she was taken from the tent," Detective Superintendent Rob Wilde told reporters on Thursday.

Cleo was last seen by her parents about 1.30am on Saturday. Her mother Ellie Smith has said she woke around 6am to discover Cleo was missing from the family's tent.

It has been confirmed the zipper on the family tent was found open to a height Cleo could not have reached, seemingly ruling out the possibility she wandered off on her own. Her red and black sleeping bag is also missing.

Acting police commissioner Col Blanch said an analysis of CCTV vision from a nearby shack had placed Cleo at the campsite on the night in question.

There have been hundreds of calls to Crime Stoppers, mostly relating to suspicious people in the area.

"This investigation is wide open," Mr Blanch said.

"We will consider any possibility ... we're hoping for answers from the community."

More than 100 police officers, as well as SES volunteers and army reservists, have been deployed to the land search in rugged terrain north of Carnarvon.

Homicide detectives have been assigned to the criminal investigation into her disappearance, dubbed Taskforce RODIA.

Supt Wilde said authorities were keeping an open mind in relation to whether Cleo may have been taken by someone known to her.

Police have not ruled out the possibility Cleo may have been taken across interstate borders.

"We've been in touch with all jurisdictions around Australia," Supt Wilde said.

"We want to get this information out there and if anyone Australia-wide has information that could be relevant to the investigation, we ask that they call Crime Stoppers."

Premier Mark McGowan on Thursday announced a $1 million reward for information which leads to Cleo's location or to the arrest and conviction of people involved in her disappearance.

"It's a very sad situation, a very difficult situation," the premier said.

"I just urge anyone who has any knowledge of the location of Cleo, please provide that information to police and ensure that we can provide some certainty and information to Cleo's loved ones and hopefully bring Cleo back safe and sound."

Investigators have spoken to up to 20 registered sex offenders in the Carnarvon area, but there are currently no suspects.

Detectives are also re-examining nearby shacks along the coastline as the search enters its sixth day.

The family are Carnarvon locals and are understood to have been camping in the same vicinity as people they knew.

Cleo's mother earlier this week said the little girl would never wander off on her own and someone must know where she is.

"She would never leave us, she would never leave the tent," Ms Smith said, describing Cleo as a beautiful and delicate girl with "the biggest heart".

Australian Associated Press