Prime Minister Anthony Albanese has described the disappearance of two Australian brothers in Mexico as "a really concerning situation".
Callum and Jake Robinson are believed to have gone missing in the country's northern Baja California region over the weekend.
This is what we know so far.
Who is missing?
Jake and Callum Robinson — both aged in their 30s — are originally from Perth.
Callum had been living in the United States for several years, where Jake had been visiting him.
Callum is a type one diabetic and there are concerns for his health.
The brothers were travelling in Mexico with an American citizen, Jack Carter Rhoad, who is also missing.
A missing persons poster is being circulated by the brothers' friends and family in the hopes it can help locate them. Source: Supplied
Where did they go missing and when?
The brothers were on a surfing and camping trip near Ensenada when they disappeared, according to a social media post from their mother, Debra.
They were due to travel to the coastal city of Rosarito earlier this week but didn't turn up to their accommodation, she said.
Their family and friends say they haven't heard from them since the weekend.
"Part of the concern is that they've been travelling through America ... and they had posted fairly regularly about their trip up until the weekend," one of the brothers' friends, Dan, told ABC Radio Perth on Thursday.
"I believe Callum was due back at work last week and hasn't shown up, so obviously friends and family are quite concerned."
What do Mexican police say?
Mexican police say they have questioned three people in relation to the men's disappearance.
One is a woman and two are men. The woman is believed to have been found with a mobile phone that contained a photo that looked like one of the brothers.
Baja California's chief prosecutor María Elena Andrade Ramírez said abandoned tents and other evidence had been found at the site where the missing men had last been seen that linked the three people police questioned to the case.
But she would not specify whether they were suspects or witnesses — or if drug cartels, which are active in the area, could be involved in the men's disappearance.
"All lines of investigation are open at this point. We cannot dismiss any of them until we find the whereabouts of these people and establish what happened in this case," she told reporters on Thursday local time.
Jake (left) and Callum Robinson (right) haven't made contact with their family since Saturday. Credit: Instagram
Others also reported a truck belonging to one of the brothers was found burnt out on a ranch.
Andrade Ramírez said the men weren't officially reported missing until a few days after friends and family lost contact, suggesting it may make it more difficult to find them.
"Important hours were lost," she said.
What has the reaction been in Australia?
Albanese said Department of Foreign Affairs and Trade officials had been in contact with the brothers' family following their disappearance.
"This is a really concerning situation," he told Seven's Sunrise program on Friday.
"Our embassy in Mexico is working with local authorities as well to try to ascertain what has happened here.
"We certainly hope that these brothers are found safely but there is real concern about the fact that they've gone missing. Their mother is obviously very distressed about this and we just hope for a positive outcome."
Prime Minister Anthony Albanese said the men's disappearance was a "really concerning situation". Source: AAP / Mick Tsikas
"I want to emphasise that my personal thoughts, and the thoughts of all of us, are with the families of the missing men," she told reporters on Friday.
"We are obviously deeply concerned."
Western Australian Premier Roger Cook said the men's disappearance was "very worrying".
"When we do send our young men and women overseas to enjoy that adventure holiday, they invite an element of risk and this is really quite distressing," he told reporters on Thursday.
Additional reporting by Australian Associated Press
