The 65-year-old man, who has not been named, was reportedly swimming about 60 yards off the beach on the Kaanapali Shores area in western Maui.
A witness in a neighbouring hotel reportedly raised the alarm and the County of Maui Department of Fire and Public Safety sent a jet ski and helicopter to find the man and bring him to shore.
They reportedly performed CPR, but the man was pronounced dead at the scene.
His death is the sixth shark-bite case of the year in Hawaii and the first to result in a fatality since 2015, according to the state Department of Land and Natural Resources.
Only five fatal shark attacks have been recorded since 1995 in Hawaii.
The weather was calm and the water was clear at the time of the attack, which happened just before 9am on Saturday.
Shark expert Michael Domier told KHON2 News: “Your chances of getting attacked by a shark and even surviving is less than one in 12 million.”
In 2015 a woman was killed by a tiger shark while swimming off Maui.
The species of shark which killed the man has not yet been confirmed.
Sharks kill about six people a year on average around the world, according to the International Shark Attack File (ISAF).
In 2018 four people died from shark attacks.
Many more people are injured and killed on land while driving to and from the beach than by sharks in the water, the ISAF notes.
“Shark bites globally are on a slow, gradual rise, a direct result of the increasing number of people in the water. But fatality rates worldwide have been on the decline for decades,” the site says.
“The somber truth is that most of the world’s shark populations are in decline, or exist at greatly reduced levels, as a consequence of overfishing and habitat loss,” the website says.
“Fisheries kill about 100 million sharks and rays annually.”