The fifth Harry Potter book has broken UK sales records, selling more than 1,777,000 copies on its first day, according to estimates.
About 13 million copies of the book were printed before Saturday
The huge numbers of The Order of the Phoenix were based on provisional figures received by 0900 BST Monday from Saturday's sales through bookshops, supermarkets, internet sites and newspapers, said sales monitoring group Nielsen BookScan.
Five million copies were sold in the US on the first day of release.
The previous UK record was set by the book's predecessor, The Goblet of Fire, which sold 372,775 copies on its first day in July 2000.
Nielsen BookScan said final sales figures for the first day's trading would be made available on Tuesday.
The company said more than 13 million Harry Potter books had now been sold in the UK.
Demand was high in countries where English is not the first language
The first Potter book, The Philosopher's Stone, is the best seller so far with more than 3.3 million sales.
The largest book retailer in the US, Barnes and Noble, sold almost 900,000 copies on Saturday, while American branches of Borders reached 750,000.
"The sales of Harry Potter and the Order of the Phoenix surpassed our expectations," Barnes and Noble chief executive Steve Riggio said.
Potter UK book sales
The Philosopher's Stone 3,371,090
The Chamber of Secrets 2,809,856
The Prisoner of Azkaban 2,655,787
the Goblet of Fire 2,865,477
The chain sold up to 80 copies per second, it said.
When former first lady Hillary Clinton sold 600,000 copies in one week earlier in June, that was hailed as a publishing phenomenon.
In the UK, an average of 220 copies of the Potter book were bought at Tesco supermarkets every minute on Saturday.
"This book broke our pre-release sales record so we knew it was going to be popular with our customers, but the sales have exceeded all our expectations," a spokesperson said.
"The book has now broken all our sales records and there is no doubt that this will be the best selling book we have ever stocked."
HARRY POTTER AND THE ORDER OF THE PHOENIX
13 million copies printed before release
One copy sold for every 60 people in US and UK on Saturday alone
One US chain sold 80 copies per second
1.3 million pre-orders taken by Amazon
Royal Mail delivered 500,000 copies in the UK
Another supermarket, Sainsbury's, said it had sold twice as many book as expected.
"It's our fastest and biggest selling book ever," an official said.
A spokeswoman for the WHSmith chain said: "It's the fastest selling book we've ever had," adding that the new novel was 10 times more popular than the last instalment.
Barbara Marcus, president of Potter's US publisher Scholastic, said: "It is extraordinary to publish this magical book which is being
read by millions of children and adults across the country at this very moment.
"Jo Rowling has once again written a novel that will be treasured by many generations to come."
Internet retailer Amazon revealed that it took orders for 1.3 million books globally.
Around the world, book stores from Bucharest to Beijing reported high demand, even though the book is available in English.
Before Saturday, almost 200 million copies of the first four books had been sold in 55 languages.