The victim was identified as 65-year-old Thomas Smiley of Granite Bay, California, Lt. Gregg Okamoto of Maui Police Department said Sunday.
Shark warning signs were posted Sunday in the Ka'anapali Beach Park area on Maui where he died a day earlier.
SEE ALSO: Houston model bitten by shark while swimming in the Bahamas
Witness Allison Keller told Hawaii News Now that Smiley appeared unconscious as rescuers pulled him from the water and performed CPR Saturday morning.
"As we got closer, I saw some blood on his stomach and then I got looking a little bit more and his wrist, it looked like the skin on his wrist was just torn off," Keller said. "And then I got looking closer and his entire left leg from his knee down was just missing."
RELATED: Man bitten in apparent shark attack on Crystal Beach
Smiley was swimming about 60 yards from shore when the attack happened, according to authorities.
The last fatal shark attack in Hawaii was in 2015, when a snorkeler off Maui was killed.