Concerns are growing over the missing Australian brothers in Mexico

Mexican investigators have warned that crucial hours have been lost in the search for two missing Australian brothers, with foul play cannot be ruled out as a possible factor.

Perth siblings Callum and Jake Robinson, both in their 30s, were on a surfing holiday on the country’s Baja Peninsula when they failed to check into pre-arranged accommodation near the city of Ensenada.

Their mother Debra Robinson appealed for help finding her two sons and an American friend they were traveling with, saying she had not heard from them since Saturday.

A ute with a surfboard in the back.A ute with a surfboard in the back.

The Perth brothers were driving this car when they disappeared. (supplied/MONKEY PHOTOS)

“Callum has type 1 diabetes, so there is also a medical problem,” she wrote on Mexican social media.

Baja California state chief prosecutor María Elena Andrade Ramírez said police have questioned three people in connection with their disappearance, but the chances of finding the men have diminished due to delays in the investigation.

“Unfortunately, their disappearance was only reported in the last few days, so very important hours have been lost there,” she told a news conference in Mexico.

Investigators have found a burnt-out white ute and abandoned tents believed to belong to the missing men.

Officials from the Department of Foreign Affairs and Trade have provided support to the family.

The department has urged people to exercise extreme caution when traveling to Baja California “due to the threat of violent crime.”

Drug cartels are known to operate in the region and the state’s chief prosecutor said “all lines of investigation” remained open.

In 2015, Western Australian surfers Adam Coleman and Dean Lucas were murdered, allegedly shot by gang members in the neighboring Sinaloa region, before their van and bodies were burned.

Australian Prime Minister Anthony Albanese, as well as opposition foreign spokesman Simon Birmingham and WA Prime Minister Roger Cook, expressed concern for the surfers’ safety and wishes for their safe return.