An unpublished Charlotte Bronte manuscript is expected to sell for between £200,000 and £300,000 at auction next month.

The Young Men’s Magazine, Number 2, was written when Charlotte was 14, and is set in Glass Town, the earliest fictional world created by the Bronte siblings.

The book contains more than 4,000 words on 19 pages, each measuring approximately 1.4in (35mm) by 2.4in (61mm).

It is dated August 1830 – 17 years before she wrote Jane Eyre – and is said to have never before been seen by scholars.

Sotheby’s said it is the most important Bronte manuscript to appear at auction in more than 30 years and is one of only a handful of such pieces remaining in private ownership.

Gabriel Heaton, Sotheby’s senior specialist in the books and manuscripts department, said: “Crafted with extraordinary care, this minute manuscript marks Charlotte Bronte’s first burst of creativity and, significantly, provides a rare and intimate insight into one of history’s great literary minds.”

Charlotte was a prolific writer as a child and later claimed that she had written more before the age of 13 than afterwards.

As an adult, her debut novel Jane Eyre was an immediate best-seller when it was published in 1847. Two years later the publication of Shirley cemented her reputation, and the publication of Villette in 1853 enhanced her celebrity.

Charlotte Bronte died in March 1855 in the early stages of pregnancy, only nine months after her marriage to her father’s curate, Arthur Bell Nicholls.

The manuscript is being sold at the auction of English Literature, History, Children’s Books and Illustrations on December 15.