The Mexican husband of missing Australian woman Tahnee Shanks, whose two-year-old girl was found wandering alone in the central American country, is "on the run", her brother says.
Mexican authorities have issued alerts for the 32-year-old Queenslander and her husband Jorge Luis Aguirre Astudillo, also 32, who haven't been seen since Monday.
The alarm was raised after the couple's toddler Adelynn was found wandering the streets alone near a church in the resort city of Cancun in the country's east.
Ms Shanks' brother Dan says 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."
The Department of Foreign Affairs and Trade told AAP it was providing consular assistance to Ms Shanks' family, but declined to comment further.
Premier Annastacia Palaszczuk said any Queenslander missing overseas is a concern, with Police Commissioner Katarina Carroll adding state police services will liaise with the Australian Federal Police on Ms Shanks' disappearance.
"If it involves someone who should be coming home, was in Queensland, we would be somehow involved in that to find out what's going on and to get some answers back to that family," the commissioner said.
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.
"I'm assuming he's dumped the car and got some other form of transport, and he's on the run," he said.
"So if he's capable of doing that to his daughter, well, that's what we're so worried about."
Ms Shanks and Adelynn had been planning to fly back to Queensland on June 16, according to her family.
Mr Shanks said he only found out about the situation through social media, when a friend sent him a picture of Adelynn outside the church, asking "is this your niece".
"We were woken up in the middle of the night and confirmed that it was," Mr Shanks added.
"And we haven't been able to get in touch with my sister, so we've got grave concerns for her safety."
Adelynn is currently being cared for by Mexican child welfare authorities (DIF) and Ms Shanks' other brother and mother are planning to fly to Cancun.
They will try to bring the two-year-old, who has Australian citizenship, back to Queensland with them.
"Adelynn's safe and being looked after at the moment, she's at the DIF in Cancun," Mr Shanks added.
"We've had the (Australian) Embassy send us photos of her and where she's staying.
"She's clothed and looked after and, yeah, looks in good health."
According to her Facebook profile, Ms Shanks, from Conway Beach in the Whitsundays, had been trying to get home after her plans were apparently delayed by the coronavirus pandemic.
She wrote in May 2021: "I can't come back to Australia till mid 2022!!! My baby girl will be 2 1/2 years old and hasn't even met her grandad, uncles, great gran, cousins."