Fears are growing for three tourists who have gone missing while on a surfing vacation in one of Mexico’s most violent states.

Australian brothers Jake and Callum Robinson and an American friend named unofficially as Jack Carter Rhoad failed to show up for an Airbnb booked in the Pacific resort of Rosarito, in the northwestern state of Baja California last Saturday.

Since then, police have found what they believe are the trio’s tents, car and a cellphone on a nearby beach.

They are also questioning three unidentified Mexican citizens, although it is unclear whether they are suspects or witnesses.

“There’s a lot of information we can’t make public. We don’t know what condition they’re in,” said María Elena Andrade Ramírez, the chief prosecutor of Baja California.

Concerns about the three first emerged on Wednesday when Jake and Callum’s mother Debra posted on a Facebook community page for foreigners visiting Baja California asking for help to locate her sons.

She said Callum, 33, a member of Australia’s national lacrosse team who lives just over the border in San Diego, is a diabetic who needs daily medication. Jake, 30, a doctor, was visiting his brother.

The US embassy in Mexico City has confirmed that a US citizen has also been reported missing in Baja California but has yet to confirm whether it is Mr Carter Rhoad.

Baja California has long been a hub of drug cartel activity. The state’s largest city, Tijuana, which is separated from San Diego by a wall, is notoriously violent. It also hosts raucous nightlife and offers cheap plastic surgery for Americans who often daytrip across the border.

The drug gangs usually avoid targeting tourists, something that would trigger repercussions from Washington. But Baja California is awash with guns bought north of the border and foreigners there can often fall prey to common crime.