Mexican authorities have discovered a fourth body in addition to the three found in a popular Mexican tourist area where an American and two Australians suddenly vanished last week.

The three dead bodies found in Mexico's Baja California state are highly likely to be the American and two Australian tourists who went missing last week, a senior official from the region said on Saturday.

Three unidentified mud-covered bodies have been recovered from a shaft in Mexico near where three surfers – two Australian brothers and an American – went missing in one of the country’s most violent states several days ago.