Speaking exclusively to Sky News, Amelie Osborn-Smith, from Andover, said: "You just never imagine it could happen to someone like you."

Miss Osborn-Smith, who was white-water rafting in Zambia, says she was swimming backwards towards her raft when she felt something go over her legs which she initially thought was her friend.

She said: "I turned to look and I realised my friend was in line with my head instead of my legs, and that's when I looked down and saw the crocodile."

She added that she saw the animal "go underneath and round to try to measure the size of me", but didn't have time to think before it dragged her underwater.

Miss Osborn-Smith said she couldn't breathe but her friend clung on to the shoulders of her life jacket while she kicked the crocodile.

"You just think how do I get out? How do we escape this? At that point, I was just so ridiculously grateful that my friend was in the water," she said.

She is planning to go back to Zambia and help build a school for the locals she met.

She said: "It brings positivity to the whole thing, which otherwise would be seen as really negative. It's something that helps me get through every day."

She said the motivation of fundraising is "pulling her through every operation and treatment" if she can "change hundreds of lives" by nearly losing her own "it will all have been worth it".

Miss Osborn-Smith added that she felt safe before the attack because well-known companies were organising rafting activities in Zambia, and she wanted to "see the world" on her gap year.

She said: "You just think nothing bad can happen, they literally do this three times a day for the last 30 years."

The hardest part of the experience for the teenager was waiting 45 minutes with no pain relief for a helicopter rescue.

She said: "No one could get signal and when you're lying on the side of a rock, and you're trying not to bleed to death, you just think how will I get through this?"

She remembers her friend holding her hand and telling her "don't look at your legs", but she told him: "It's okay, tell them to amputate both my legs."

She added: "I looked down and I knew in my head that there was no saving my legs and I said that it's fine. I nearly lost my life, losing my legs compared to that is nothing."

Miss Osborn-Smith said she was worried about crying because she was losing blood and might pass out, but when she was onboard the rescue helicopter she "burst into tears".

"You don't realise until you're back how much you've actually gone through," she said.

She has had seven operations, and will likely have more, but can now walk on crutches.

The teenager, who is hoping to start university in September, said she feels "unbelievably grateful".

"Obviously what happened was terrible, but I can't change it and I was so lucky to have people around me I did. It's kind of a reality check, and makes you realise how lucky you are and how amazing life is," she added.

She hopes her efforts to build a school in Zambia will help 104 children from the villages of Muke and Delevu, which she visited on her trip.

She said: "They were the nicest people in the world. They don't have a school and this story has had so much attention, I just hope that something good to come out of it."

To donate to Miss Osborn-Smith's campaign to build a pre-school in Zambia, visit her fundraising page here.