A hitherto unknown portrait believed to be of author Emily Bronte is expected to fetch thousands of pounds when it goes under the hammer this week, Huffington Post reported.

The oil painting is the latest in a flurry of items relating to the Bronte sisters to be put up for auction in the last few months.

Its sale by JP Humbert's in Northamptonshire comes after the auction house sold another painting of the reclusive writer for £23,836 in December.

Auctioneer Jonathan Humbert said the 33 by 24cm (13 x 9.5 inc) painting has already attracted international interest after the previous sale - which originally had a guide price of £10,000 - £15,000.

The second painting, which is annotated Emily Jane Bronte, was originally estimated to fetch around £3,000 but, after growing interest, now has an estimate of £5,000-£8,000 for its sale on Thursday, February 23.

In December an unpublished manuscript by sibling Charlotte Bronte was sold at auction to a Paris museum for a record value of £690,850 at Sotheby's.

Sotheby's estimated it would sell for between £200,000 and £300,000, but the manuscript sold for more than double the top estimate, setting new auction records for a manuscript by Charlotte Bronte and for a literary work by any of the Bronte sisters.

It was bought by Paris museum La Musie des Lettres et Manuscrits, scuppering attempts by the Bronte Society to return it to the Bronte Parsonage Museum at the writer's home in Haworth, West Yorkshire.