A 10-year-old girl who survived being stung by the world's most venomous creature — the deadly box jellyfish — may have rewritten medical history, an expert has said.

Rachael Shardlow from Australia lost consciousness after being badly stung by the jellyfish while swimming in a river with her brother in December.

"When I first saw the pictures of the injuries I just went, 'You know, to be honest, this kid should not be alive,’” zoology professor Jamie Seymour, from James Cook University, told ABC News in Australia. "I mean, they are horrific. Usually when you see people who have been stung by box jellyfish with that number of the tentacle contacts on their body, it's usually in a morgue."

Often deadly, the box jellyfish has long, trailing tentacles and is able to squeeze through even the smallest of nets as it is only the size of a fingernail.

The venom is so overpoweringly painful that victims often go into shock and drown or die of heart failure before reaching the shore. There is no effective anti-venom for its sting, which attacks the heart, nervous system and skin, inducing shooting muscle pain, vomiting and a rapid rise in blood pressure.

Rachael was pulled from the Calliope River, near the town of Gladstone, by her 13-year-old brother with the jellyfish's tentacles wrapped around her legs.

Before passing out, she told him she could not see or breathe.

After the rescue, she spent six weeks recovering in hospital before returning home.

"I don't know of anybody in the entire literature where we've studied this where someone has had such an extensive sting that has survived,” Seymour said. "From our point of view, it's really useful information that you very seldom, if ever, get your hands on."

The girl's father Geoff Shardlow told ABC News that his daughter had suffered scarring to her legs and some short-term memory loss.

Click here to read mor from Sky News.