MILAN (AP) — Italian prosecutors today opened a criminal investigation into the deaths of at least 10 people swept away by a flash flood as they hiked through a narrow gorge in the southern region of Calabria.

Italy’s civil protection agency said at least three people were missing, although the number could be higher since guides were not mandatory inside the Raganello Gorge, a popular spot for aquatic trekking.

Rescue workers saved 23 people Monday after some 2 1/2 meters (8 feet) of rain filled the narrow gorge, which features rock faces as high as 700 meters (2,300 feet). Eleven people were hospitalized, including a 10-year-old boy treated for hypothermia.

Prosecutor Eugenio Facciolla said authorities were investigating possible charges including manslaughter, causing bodily harm and official negligence, the news agency ANSA reported. No target has been identified.