American tourist Albert Calibet missing for several days on the Greek island of Amorgos

Greek authorities are searching for an American tourist who went missing after hiking alone on the island of Amorgos.

Local authorities say Albert Calibet, 59, has been missing since Tuesday afternoon. His friend reported him missing when he did not return from his hike.

Several agencies are involved in the search for Mr Calibet, including coast guard volunteers and teams from the neighboring islands of Paros and Naxos, according to Greek public broadcaster ERT News.

His disappearance comes a few days after that of British television presenter Michael Mosley on the Greek island of Symi, where his body was found four days later.

The BBC has contacted the US State Department for comment.

Authorities are searching both land and water in an area covering almost a quarter of Amorgos, the island's mayor, Eleftherios Karaiskos, told ERT.

They use a drone to search the northern part of the island and also try to find Mr. Calibet's two cell phones. Calls to Mr Calibet – who the mayor said had already been to the island – went unanswered.

“We're almost three days here,” his brother Oliver Calibet told Fox 11 TV in Los Angeles. “There’s no water…I’m very upset.”

The island's mayor said the hike Mr. Calibet embarked on was busy and not particularly difficult, suggesting the American may have changed his planned route.

Mr. Calibet, described as a retired Los Angeles County police officer, began a four-hour hike around 7 a.m. local time (12 a.m. EDT) in the village of Aegiali on Tuesday, according to local media.

A few minutes later, he allegedly sent a text message with a photo of the sign indicating the route he was taking to get to Katapola, a roughly four-hour walk.

Around 9 a.m., a local woman said she spoke to the missing tourist after he bought drinks at a nearby store. Sofia Liviaki told Mega TV that Mr Calibet drank a soft drink, showed her his planned route and took a bottle of water with him for the rest of his trip.

Mr Calibet's disappearance has shocked the local community of Amorgos, where he has visited regularly for several years. Although the path he chose was well traveled and easy, the island experienced a heatwave with temperatures currently reaching 35°C.

“Temperatures are very high, like throughout Greece during the heatwave,” Popi Despotidi, the island's deputy mayor for tourism, told Greek media. “We think he felt dizzy… and collapsed somewhere. It's strange because he's not someone who was traveling this road for the first time.”

The search for the missing man comes just days after authorities spent days scouring another Greek island, Symi, in search of Dr Mosley, a famous British TV doctor who disappeared after going for a walk from a beach.

His body was found in a rocky area and investigators concluded he died of natural causes on the day he disappeared.