“We heard screaming from the water and it was this unbelievable scream like I’ve never heard before,” Andree Conley-Kapoi, a witness to the attack, told Maui News Now.
“The only time anybody would scream like that is if they are being attacked by a shark,” Conley-Kapoi said.
The incident is Maui's fifth such attack this year.
After witnesses called for emergency services she was taken to Maui Memorial Medical Center where she remains in critical condition.
"Her right arm was severed right below the shoulder,” Maui Fire Services Chief Lee Mainaga told reporters. "The arm was not found."