A shark attacked and killed an American woman along a beach in St. Croix in the U.S. Virgin Islands, officials said Friday.

Police identified the victim as 56-year-old Arlene Lillis of Minnesota. A hometown wasn’t immediately available.

Authorities said the attack occurred close to shore on western St. Croix on Thursday afternoon.

Police and other emergency crews responded to the beach, where crews worked “swiftly and professionally under very extreme and difficult circumstances” to treat Lillis, said Daryl Jaschen, director of the Virgin Islands’ emergency management agency.

Lillis, who was a frequent visitor to the U.S. territory, was taken to a local hospital for further treatment but died from her injuries, according to Lt. Gov. Tregenza A. Roach.

Police said they were initially told there may have been a second victim, but a perimeter search by authorities did not discover any other victims.

Officials said they have not yet confirmed what type of shark was involved in the attack. They said that while shark sightings are common, attacks in the U.S. Virgin Islands are unusual.

“Encounters that result in a bite are very rare,” said Nicole Angeli of the U.S. Virgin Islands Department of Planning and Natural Resources at Friday’s news conference.

She said Thursday’s attack was the second such incident in a decade, and that there are plans to put up more signs and share more information at hotels and beaches on how to be safe around wildlife.

Jaschen, of the emergency management agency, said the investigation into the attack is ongoing, and that he could not immediately say what may have caused the shark to come so close to the shore.

Overall, at least 79 unprovoked shark attacks have been reported in the Caribbean since 1749, including four in the U.S. Virgin Islands, according to the Florida-based International Shark Attack File.