Sheriff's spokeswoman Teri Barbera said the dogs allegedly escaped their fenced enclosure and had been wandering around before the Wednesday morning attack, the Palm Beach Post reported.
The victim's name has not been released.
Bystanders beat off the animals until sheriff's deputies arrived and shot, wounding the dogs.
Animal Care and Control is handling both animals, the Post reported.
Barbera said it's unclear how the dogs got loose, to whom they belong, and if charges are filed who would file them, Animal Control or the Sheriff's Office.
Swim Week Miami Beach 2014 [PHOTOS]