The girlfriend of a US man who savagely used his bare teeth to rip into another man's face in Florida said he must have been under the influence of drugs or voodoo magic, local media reported on Thursday.

The naked assailant, 31-year-old Rudy Eugene, was shot dead by police in Miami on Saturday after consuming almost the entire face of his victim, a 65-year-old homeless man.

Eugene's girlfriend, who asked not to be identified, told the Miami Herald that the man who carried out the attack bore no resemblance to the gentle man she was dating, and surmised that Eugene might have unwittingly been under the influence of drugs.

"The only other explanation was supernatural — that someone put a voodoo curse on him," the woman told the daily of Eugene, who is of Haitian descent.

"I don't know how else to explain this," she said. "He was a believer of God."

Eugene's mother, Ruth Charles, also subscribed to the theory that her son was under the influence of powerful drugs.

"Everybody says that he was a zombie, but I know he's not a zombie; he's my son. I don't know what they injected in him to turn him into the person who did what he did," she said.

News reports said the victim, identified as Ronald Poppo, remained in hospital in serious condition.

Saturday's bloody spectacle unfolded near Miami's busy MacArthur Causeway, a low-slung bridge from the downtown area to nearby beaches.

Police ordered Eugene to stop his assault, and then fatally shot him when he continued to devour the face of his victim.

Poppo reportedly lost 75 percent of his face in the attack, including his eyes, nose, cheeks and mouth.