Clinton is on a book-signing tour of the US

Barnes and Noble, one of the US's biggest book retailers, said the record was set after it sent out more than 40,000 copies to its stores and online customers in the first 24 hours.

First-day sales for the memoirs, called Living History, were said to be more in keeping with best-selling fiction than a political memoir.

The 562-page book looks set to become the biggest non-fiction title of the year in the US.

Mrs Clinton's memoirs reveal her husband lied to her about the Lewinsky affair

Mrs Clinton's publisher, Simon and Schuster, said: "By our estimates, we sold at least 20% of the one million-copy first printing on Monday."

Living History includes Mrs Clinton's thoughts on her husband Bill's infidelity with White House intern Monica Lewinsky.

It is the first time she has publicly aired her opinions on the matter.

"As a wife, I wanted to wring Bill's neck," she wrote.

And Mrs Clinton, who was paid $8m (�5m) for the memoirs, admitted that she and her husband had subsequently slept in separate beds.

Reprints ordered

She is now a first-time senator from New York for the Democrats, although her memoirs revealed her early politics were closer to the opposing Republicans.

Simon and Schuster has ordered reprints totalling 300,000 copies and said it expected to order more later this week.

Mrs Clinton was First Lady for eight years from 1992 to 2000.

She leaked many of the book's key revelations in interviews the day it was published.