One of two children bitten in the leg off New York’s Fire Island was attacked by a shark, officials have confirmed.

The state department of environmental conservation said a tooth fragment removed from a 13-year-old boy’s leg belonged to a shark, although inquiries could not pinpoint which species was responsible.

Officials could not confirm if the fish responsible for attacking a 12-year-old girl a few minutes before the boy at Sailors Haven beach was also a shark.

People on the beach on Fire Island
People enjoy the beaches on Fire Island in Islip, New York (AP)

Both children were bitten on Wednesday, prompting officials to temporarily close the beaches.

The youngsters are expected to fully recover.

The state parks department is extending lifeguard coverage until later on Friday, and drones will be deployed to monitor the waters.