A team of marine conservationists has captured a face-to-face encounter with a massive great white shark near the Hawaiian island of Oaha.

Diver Ocean Ramsey, who swam with the shark and placed her hand on its back while filming the experience, claimed its size and markings suggest it could be Deep Blue – one of the largest great white’s ever recorded.

Ms Ramsey and her team had been in the area to film tiger sharks feeding on a dead sperm whale carcass when the great white arrived unexpectedly. The conservationist estimated that the “gentle” shark was more than 20ft long and 8ft across.

“She was just this big beautiful gentle giant wanting to use our boat as a scratching post,” Ms Ramsey told the Honolulu Star-Advertiser. “We went out at sunrise, and she stayed with us pretty much throughout the day.”

The surprise rendezvous prompted state officials to warn amateur divers to keep clear of the “dangerous” area, amid reports some had climbed onto the nearby dead sperm whale to take its teeth as souvenirs.

Chief Jason Redull, of Hawaii Department of Land and Natural Resources, said people should stay out of the water around the dead whale.

“We don’t want anyone to get hurt if a shark swimming around the carcass mistakes them as food. Understandably, some people want to get into the water either out of fascination or to get photographs, but it is truly dangerous to be around this carcass with so much shark activity,” he said.

Ms Ramsey was criticised more directly by the great white shark researcher Dr Michael Domeier. He wrote in an Instagram post: “The number 1 rule of legitimate shark diving operators is DON’T TOUCH THE SHARKS! Posting selfies with white sharks is really the wrong message… these are very dangerous animals.”

Diver Ocean Ramsey swims next to female great white shark (AFP/Getty Images)

Deep Blue is believed to be one of the largest great white sharks in the world. Ms Ramsey previously swam with the huge shark on research trips to Guadalupe Island, Mexico. As well as studying sharks, she advocates for their conservation and leads cage-free shark diving tours.

“Big pregnant females are actually the safest ones to be with you – the biggest, oldest ones – because they’ve seen it all, including us,” she said. “That’s why I kind of call her, like, a grandma shark.”