Homeless man Ronald Poppo has been identified as the victim in the horrific Miami attack in which 31-year-old Rudy Eugene chewed off large portions of his face.

Police shot and killed Eugene after he refused to stop chewing on the face of Poppo by the MacArthur Causeway in Miami.

Poppo, 65, remains in a critical condition in hospital. He is reported to be a homeless man who lived underneath the causeway.

Miami police sergeant Armando Aguilar told the Associated Press: "He had his face eaten down to his goatee. The forehead was just bone. No nose, no mouth.

"He just happened to be in the wrong place at the wrong time."

CCTV footage show the men, who were both naked at the time, lying next to the busy highway at around 2pm local time.

Sgt Javier Ortiz said it was one of the "goriest scenes I've ever been to.

"It was not only grotesque, it was just very sad, the amount of blood. It was very sad to see what happened to this gentleman that had his face eaten," Ortiz said.

Larry Vega, an eyewitness who first called the police about the incident, described how Eugene was eating Poppo "like a zombie" during the attack.

"The guy was like tearing him to pieces with his mouth, so I told him, 'Get off!'" he told WSVN in an interview.

"He just kept eating the other guy away, like ripping his skin. The police officer came over, told him several times to get off, and an officer climbed over the divider and got in front of him and said: 'Get off!'

"He told him several times and the guy just stood his head up like that with a piece of flesh in his mouth and growled. The guy, he was like a zombie, blood dripping. It was intense."

The reason Eugene attacked Poppo is still not known. Authorities believe Eugene may have suffered drug-induced psychosis either from LSD or synthetic stimulant drugs such as bath salts.