A giant squid has been caught on camera grabbing at a lure attached to a deep sea research vessel, with scientists saying it is the first time one has been filmed in waters off the southern coast of the United States.

Key points: The scientists who filmed the squid believe they were able to do so due to their unobtrusive research vehicle

The scientists who filmed the squid believe they were able to do so due to their unobtrusive research vehicle The squid had never been filmed during thousands of previous submersible dives

The squid had never been filmed during thousands of previous submersible dives When the crew saw "an enormous set" of tentacles coming for their lure they knew immediately it was a giant squid

The juvenile, estimated to be up to 3.7 metres long, was spotted by an international team of scientists who had spent two weeks in the Gulf of Mexico trawling waters where the sun does not reach to see how the creatures there live without light.

Using a stealth camera mounted on an underwater research vessel dubbed Medusa, the team had been probing at a depth of about 750 metres when something emerged from the dark.

It appeared to have been attracted to the vessel's optical lure, known as an electronic jellyfish, or "e-jelly".

It was "a large tubular animal" that looked like it was hunting the e-jelly, according to Professor of Biology Sonke Johnsen and Edie Widder, an Ocean Research & Conservations Association senior scientist.

The e-jelly's lights, which are designed to mimic the bioluminescence of deep sea jellyfish. ( Supplied: NOAA )

"The tubular animal revealed an enormous set of arms and tentacles coming in to attack the e-jelly," they said.

"We knew immediately that it was a squid. It was also big, but because it was coming straight at the camera, it was impossible to tell exactly how big.

"But big — at least 3 to 3.7 meters long."

Giant squid had been thought to be able to grow up to 12 metres long, however studies using new modelling techniques suggest they may be able to reach as much as 20 metres in length.

While the animal may draw comparisons with fabled beasts of the deep sea, the team behind the vision stressed that it was not a monster.

"The giant squid is large and certainly unusual from our human perspective," they said.

"But if the video shows anything of the animal's character, it shows an animal surprised by its mistake, backing off after striking at something that at first must have seemed appealing but was obviously not food.

"What were once monsters to be feared are now curious and magnificent creatures that delight."