A US researcher has broken the world record for the longest time spent living underwater without depressurisation.

Joseph Dituri has spent more than 74 days at the bottom of a 30ft-deep lagoon in Key Largo, Florida.

And he does not have plans to stop yet. On Sunday, he said he would stay in Jules' Undersea Lodge for at least 100 days.

"The curiosity for discovery has led me here," he said.

"My goal from day one has been to inspire generations to come, interview scientists who study life undersea and learn how the human body functions in extreme environments," he added.

The previous world record for most days spent living underwater at ambient pressure - 73 - was established by two professors in 2014 in the same Key Largo lodge.

Unlike a submarine, the lodge does not use technology to adjust for the increased underwater pressure.

Prof Dituri - who goes by the nickname Dr Deep Sea - began his journey on 1 March at Jules' Undersea Lodge, a small room that sits at the bottom of a lagoon in the Florida Keys.

It is named after Jules Verne, who wrote the well-known sci-fi book 20,000 Leagues Under the Sea.

For the project, called Project Neptune 100, the University of South Florida professor is studying how the human body reacts to long-term exposure to extreme pressure.

Researchers are studying the 55-year-old's health, as well as the psychological effects of being isolated and confined for so long, by running a series of medical tests.

But his time underwater has not kept him from his professorial duties. Prof Dituri - who also served in the Navy for 28 years - is teaching his biomedical engineering classes online while he lives in the lagoon, according to the University of South Florida.

To keep busy, the professor wakes up at 05:00 each day to exercise. He stays full by reportedly eating protein-heavy meals such as eggs and salmon that he can keep warm with his microwave.

And while his underwater stay has proven ground-breaking, he is excited to get back to some above-ground activities.

"The thing that I miss the most about being on the surface is literally the sun," he told the Associated Press.