Inside the minds of the young Brontës

They might be known for their gothic romances, but the Brontë sisters also created some of the earliest examples of science fiction. When Charlotte, Emily, Anne and their brother Branwell were as young as 10, they wrote stories set in detailed, imaginary worlds. Now these little-known fantasy stories are being exhibited in the British Library's first sci-fi exhibition.

As with the best of childhood make-believe, the siblings became obsessed with their imaginary world, drawing maps and creating lives for their characters while featuring themselves as the gods of their world. Written on to scraps of paper and stitched together to create booklets, the works are like the early fanzines created by science-fiction fans of the 1930s. It might be wise to bring a magnifying glass, so minuscule is the handwriting. It was intended to represent the writing of the toy soldiers hailing from the countries the Brontë children created.

"They're difficult to get a grip on because they're written in very tiny handwriting – they were really for distribution among themselves," explains guest curator Andy Sawyer, director of science-fiction studies at the University of Liverpool. "The Brontës' manuscript books are one of the first examples of fan fiction, using favourite characters and settings in the same way as science fiction and fantasy fans now play in the detailed imaginary universes of Star Trek or Harry Potter. While the sense of fantasy is strong, there are teasing examples of what might be called the beginnings of science fiction."

Strange as some of the stories are, they also point to the sisters' future as authors. Charlotte carried on writing them into her 20s. "It was a way of developing their own skills as writers," says Sawyer. "It's not just childhood rubbish. Some are very melodramatic, but there's a lot of very good stuff – you can tell with some of the stories that they are going to be great writers."

They were not the only authors who created imaginary worlds in their childhood. JRR Tolkien and CS Lewis followed suit, while the exhibition also presents other works of utopian and speculative fiction that show another side to sci-fi, such as Mary Shelley's Frankenstein, George Orwell's 1984 and Audrey Niffeneger's The Time-Traveler's Wife.

Out of this World: Science Fiction but not as you know it, British Library, London, NW1 (www.bl.uk-sciencefiction) until 25 September