Mexican authorities said on Thursday they were searching at sea and on land for two Australians and one American reported missing in Baja California, one of the country's most violent states.
Australian brothers Callum and Jake Robinson and American Jack Carter Rhoad were reported missing on April 29, according to Baja California's prosecutors' office, and were last seen on April 27.
The three were on vacation surfing in the municipality of Ensenada, about an hour and a half south of the US-Mexico border.
"Since the disappearance was reported, the operation has been ongoing, and so far, a cell phone apparently belonging to one of the missing persons and a vehicle have been recovered," Jorge Argoud, operational deputy director of security in Ensenada, told Reuters.
State prosecutor Socorro Ibarra said three people are being investigated in regards to the case, though it remained unclear whether they were involved in the disappearance of the men.
Tents were found in the area the missing men were last seen, said Ibarra, adding that they were formally reported missing days after their actual disappearance.
"We have already contacted authorities in the United States and also in Australia because it is important in these cases to know the full context about the missing persons," Ibarra told journalists during a news conference.
People alleging to be related to the Australian brothers posted about their disappearance on social media last week. Relatives of the missing persons did not immediately respond to a request for comment.

US, Iran and mediators make push for 45-day ceasefire
US snatches airman from Iran as Trump, Israel ratchet up pressure
Ships near Italy rescue 32 migrants as 71 remain missing
Nigerian army rescues 31 hostages after church attack
At least 11 killed in Israeli airstrikes in Lebanon