WARNING: Distressing content.

A US Navy base worker is in critical condition after a shark attack during a lunchtime swim in Florida, with the frightening incident captured on video.

The man, believed to be in his late 20s, was attacked on Monday morning off the Florida Panhandle while swimming with a colleague during a break, Naval Support Activity Panama City said.

Footage of the attack shows the man struggling in the water as he is dragged under, while a witness can be heard screaming for “help”.

WJHJ are reporting that the victim has worked at the base for about four years.

He suffered severe injuries to both arms AND was rushed to a nearby hospital and underwent emergency surgery, where he remained in critical condition on Tuesday, WNBB reports.

Authorities, including the Bay County Sheriff’s Office, the Florida Fish and Wildlife Conservation Commission and the National Oceanic and Atmospheric Administration, are investigating the incident.

Base officials are also trying to determine who filmed the attack and how the video was circulated.

Shark bites are rare, but experts say swimmers should always take precautions when entering waters known to be home to marine predators.

Two shark attacks in same region a day apart

Meanwhile, in Brazil, a teenage girl had her leg torn off in a shark attack off a popular beach, in a shocking incident that came just one day after an 11-year-old boy was also seriously injured in a separate attack in the same region.

The latest attack occurred on last month at Boa Viagem Beach in Recife, in the state of Pernambuco, where 19-year-old Marcela Vitoria de Lima Santos was swimming with relatives and friends when she was bitten by a shark.

Witnesses say Marcela was drifting further from shore and appeared to be struggling in the water before her cousin intervened.

He swam out to her and brought her back toward the beach with help from other swimmers and bystanders.

Footage from the scene shows beachgoers gathering on the sand and assisting as she was pulled from the water and given first aid. A doctor who happened to be nearby also stepped in to treat her injuries before emergency services arrived.

She was taken to hospital for emergency treatment. Medical staff later confirmed she underwent surgery and described her condition as serious, with her leg amputated at the thigh, according to The New York Post.

Her cousin Jonas described the moment he went into the water to save his cousin and the severity of her injuries.

“I was the one who rescued her in the sea,” he said.

“I went into the water because she was drifting a little further away and losing strength. I don’t know, so I grabbed her by the arm, brought her out, pulling her, swimming back to shore, and people came and helped me.

“She was very badly injured and already without her leg.”

The incident came just 24 hours after another shark attack in the same broader area.

On Sunday, 11-year-old Joao Lucas Castor Nemezio Sales was attacked at Piedade Beach in Jaboatao dos Guararapes, part of the Recife metropolitan region.

Officials said the boy suffered serious injuries to his left hand and hip after being bitten, as reported by The New York Post.

He also lost his leg in the attack. He was taken to hospital for surgery and was conscious and in stable condition.