Twenty-eight-year-old New Zealander Eleanor Catton has become the youngest ever winner of the Man Booker Prize for her second novel, The Luminaries.

The book, at 832 pages, is also the longest to win the award.

Irish author Colm Tóibín had been shortlisted for his book The Testament of Mary.

The Luminaries tells the story of Walter Moody, who finds himself embroiled in a mystery during the New Zealand gold rush.

Chair of the judges Robert Macfarlane described The Luminaries as a "dazzling work, luminous, vast".

Commenting on her win, Catton said that hearing her name announced was like hitting "a white wall".

"I remember I'd written something down and it was in the depths of my handbag ... I've just bought a new handbag because my old one wasn't big enough to fit in my book," she said.

"It's a curious thing about writing a novel: you never see it until it's finished. When I was nearing the end I started to get a sense that when I pressed 'save' on my Word document it took an awfully long time. It wasn't until I got a proof of the book I thought, 'jeepers this is quite big'."