Two children swimming in the sea along the Fire Island National Seashore in New York suffered puncture wounds to their legs in apparent shark attacks.
Local authorities said that if confirmed they would mark the state's first such incidents in 70 years.
The victims - a 12-year-old girl and a 13-year-old boy - were discharged after emergency medical treatment, each with a bandaged right leg, and both are expected to fully recover.
What appeared to be a shark's tooth was extracted from the boy's leg and will be analysed to determine the species of the creature he encountered while boogie-boarding at Atlantique Beach in the town of Islip, officials said.
The girl, identified at a news conference with her parents afterward as Lola Pollina, said she was standing in waist-deep water at Sailors Haven beach in nearby Brookhaven, 3km east of Islip, when she was bitten.
"I saw something, like, next to me, and I kind of felt pain, and looked and I saw a fin," she said
She recounted how she realised her leg was "all bloody" as she scurried from the water. The shark she saw appeared to be about 91-122cm long, she said.
Fire Island Ocean Rescue Chief Lifeguard Craig Amarando praised the boy's calmness after the incident.
He said: "[The emergency services] came and they took our dressings off because they wanted to see the wounds.
"That's when they confirmed also, not only was it a shark bite, but they found one of the teeth still inside the boy.
"So the boy was very brave. He was alert the whole time. He was scared of course, but he was a brave boy."
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Shark attacks on humans are extremely rare in waters off Fire Island, east of New York City, or anywhere else in the state, according to Ian Levine, chief of the Ocean Beach Fire Department.
Only about ten cases of shark bites on people have ever been documented in New York state, the last one in 1948, Mr Levine said.
Neither incident has yet been officially confirmed as a shark attack, but Mr Levine added: "The tooth we pulled out of the kid's leg looks like a shark's tooth."
The attacks come in the week when experts said that new types of sharks could be heading to Irish and British waters as a result of warming seas.
A new study has revealed ten species of sharks currently found in warmer parts of the world, such as hammerheads and blacktip sharks, may be swimming in Irish and British seas within 30 years as the climate changes.