The family of missing Queensland mum Tahnee Shanks have made a tragic prediction after being reunited with her daughter in Mexico.
The disappearance of the 32-year-old mum, who hasn't been seen since Monday, remains a mystery as her relatives work tirelessly with the country's authorities to locate her.
The alarm was raised when Ms Shanks' two-year-old daughter, Adelynn, was found wandering the streets of Cancun barefoot and alone.
On Saturday, Ms Shanks' mum and brother, Daniel Shanks, arrived in Mexico and were reunited with the toddler, who they hope to bring home.
Mr Shanks said he had been messaging with his sister the weekend before she vanished, adding the communication "suddenly stopped".
"It's been pretty tough," he told Nine News.
"I've got no confidence in finding Tahnee to be honest.
"We're doing our best to keep it together."
The family issued a statement confirming Adelynn was once again with her uncle and grandmother.
"Our immediate goal is to get Addy, her uncle and grandmother home safely as soon as possible. With several hurdles and red tape this may take some time," the statement said.
"We remain deeply concerned for the safety and whereabouts of Adelynn’s mother Tahnee at this stage."
Adelynn's seen with her dad, brother claims
Ms Shanks, from the Whitsundays, has been living in Mexico with Adelynn's father, Jorge Luis Aguirre Astudillo, a Mexican citizen. He is also missing and was last heard from on Monday.
According to her brother, Mr Astudillo was seen dropping off the couple's daughter near a church and fleeing the scene.
"We've got bugger all information at the moment, but what we do know is her partner is the one who has dumped Adelynn outside the church," he told Nine Network on Friday.
"We've got three eyewitnesses telling us that, verifying it was him, and Tahnee's the one missing.
"And he's on the run, as far as we're concerned. So, it's... Yeah... Devastating."
Search for missing mum continues
Mr Shanks said local authorities have been analysing footage of a car leaving the couple's home, and other CCTV footage and pinging the couple's mobile phones to trace their last GPS locations.
The car used to drop off Adelynn was found dumped in Cancun, Mr Shanks said, increasing his concerns about his missing sister.
Ms Shanks and Adelynn had been planning to fly back to Queensland on June 16, according to her family.
The Department of Foreign Affairs and Trade told AAP it was providing consular assistance to Ms Shanks' family, but declined to comment further.
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