A signed four-page letter from George Washington to his nephew is expected to break sales records in one of two manuscript auctions at Christie's in New York today.

The letter could fetch up to $2.5 million which would smash the previous record of $834,500 set in 2002 for a Washington document.

The letter by the first President of the US was written from Mount Vernon, Washington's home for more than 45 years, on November 9, 1787.

"It is far and away the most significant and the richest in terms of content," of Washington's letters, said Chris Coover, an expert at Christies.

This is the first time the letter has been publicly exhibited, although it has already been reproduced.

In the letter, Washington shared his firm support for the ratification of the American Constitution.

"The letter is one of the most explicit and strongly worded letters regarding the Constitution," said Mr Coover, adding that the candor and passion of the letter help to explain the high price tag.

As part of the same auction, Christie's will sell a very rare manuscript of author Vladimir Nabokov's last, unfinished and unpublished novel, The Original Laura. Written from a hospital in Switzerland and saved from destruction by Nabokov's wife and son, the manuscript is written in pencil on 138 index cards.

The manuscript, which could sell for as much as $600,000, is the first manuscript by Nabokov that has been put up for auction.

At a separate sale also scheduled for today, Christie's will sell other works by famous authors such as Edgar Allen Poe and Charles Dickens.

A third auction slated for Wednesday 9 will feature rare books from travellers and explorers, including an 1845 volume of George Caitlin photographs of Native Americans, estimated to sell for up to $300,000.