Two children were bitten in the leg in the waters off New York's Fire Island in possible shark attacks, prompting beach closings, authorities said.

Suffolk County police said they were investigating the separate incidents, which occurred less than 8km apart at Sailors Haven and Atlantique beaches. Both beaches were temporarily closed.

A 13-year-old boy was bitten while on a boogie board at Atlantique Beach and was treated at a hospital, according to Town of Islip spokeswoman Caroline Smith. EMTs at the scene removed a tooth from the boy's leg.

At Sailors Haven beach, a 12-year-old girl suffered bite marks "consistent with a large fish" while wading, said Elizabeth Rogers, a spokeswoman for Fire Island National Seashore, which runs the beach.

Rogers said authorities had not confirmed the wounds to be shark bites, but said the Suffolk police marine bureau was waiting for the state Department of Environmental Conservation to identify the tooth.

Philip Pollina said he and his wife heard their daughter Lola scream, then she emerged with a bloody leg.

Pollina says lifeguards initially thought a Portuguese man-of-war had stung her but then concluded there were "teeth marks."

"I saw something next to me and I kind of felt pain and I saw a fin, I don't know how to describe it, and then I ran out of the water because I felt it," Lola said at a press conference.

"It was not that big like 3 (0.91m) or 4 feet (1.22m)."

Democratic Gov. Andrew Cuomo released a statement saying he had deployed DEC Commissioner Basil Seggos to lead a multi-agency investigation into the possible shark attacks.