Kit Roberts
Chilling footage shows a shark circling a beach as a survivor was pulled bleeding from the water in Texas.
People had been enjoying the 4th of July on the beach on South Padre Island in Texas on Thursday morning when the shark attacked.
The footage shows a dorsal fin moving back and forth not far offshore as a woman lies injured on the beach.
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Encounters with sharks are rare in Texas, and attacks rarer still marking out just how unusual the attack was.
Capt. Chris Dowdy of the Texas Parks and Wildlife Department said that the department believes a shark around six feet long was responsible.
The department added that shark attacks on humans are usually a case of mistaken identity, with the predators mistaking humans for prey animals.
A woman pulled to shore was one of two people who were bitten in the attack.
Officials confirmed that two others encountered the shark in the water: one was grazed and another injured fending off the shark.
The images show blood pouring into the water as the injured swimmer is hauled ashore.
A statement from Texas Parks and Wildlife said: "Details at this time indicate that two people were bitten and two people encountered the shark but were not seriously injured.
"The two victims who were bitten were transported to Valley Regional Medical Center in Brownsville where one is being treated and the other has been flown out for further treatment.
"Local game wardens and members of the Texas Game Warden Marine Tactical Operations Group assisted in patrolling the beach by boat and land patrol while DPS patrolled the area by helicopter and SPI PD and Cameron County rangers assisted with crowd control on the beach. No further details are known at this time."
Dr Kelsey Banks is a scientist at the Center for Sportfish Science and Conservation, and told CBS News that the footage suggests that the shark was of a larger species.
"Larger coastal species have been known to increase feeding behaviors and remain closer to shore prior to large meteorological disturbances," Banks wrote.
The two people bitten by the shark have been transported to the Valley Regional Medical Center in Brownsville, with one being flown for further treatment.
There are hundreds of species of shark, but only a small number of species are responsible for the majority of attacks on humans.
These include the Great White, the Tiger Shark, the Bull Shark, and the Oceanic Whitetip Shark, among others.