A never-seen-before story by Katherine Mansfield has been discovered among papers recently acquired for the world's largest Mansfield collection in Wellington.

After more than two years of negotiations with family of the writer's husband, John Middleton Murry, Alexander Turnbull Library became the proud host of six boxes of documents in August.

Many of the papers had never been seen publicly before, including correspondence with literary giants, family photographs, her passport, and a letter telling a princess to back off from her husband.

Details around the discovery of a new Mansfield story will be revealed at an announcement at the National Library today.

Gerri Kimber, the United Kingdom expert who discovered the complete short story and other poems by Mansfield, will present the find to coincide with a Mansfield conference that was held in Wellington at the weekend.

She is the same Mansfield expert who endorsed four of the writer's short stories discovered by a PhD student at London's King's College last year.

A spokesman for the Department of Internal Affairs, which is responsible for the National Library, said the story was "obviously an immensely important find" and had created much excitement at the library.

Mansfield died of tuberculosis in 1923. She remains one of New Zealand's best-known authors for her short stories, such as The Garden Party and The Fly.

She grew up in Wellington, but left New Zealand to pursue her literary career in Britain.

- © Fairfax NZ News