It is the richest going-away party in history.

“Harry Potter and the Deathly Hallows,” the seventh and final volume of J.K. Rowling’s all-conquering fantasy series, sold a mountainous 8.3 million copies in its first 24 hours on sale in America, according to Scholastic Inc.

No other book, not even any of the six previous Potters, has been so desired, so quickly. “Deathly Hallows” averaged more than 300,000 copies in sales an hour — more than 50,000 a minute. At a list price of $34.99, it generated more than $250 million of revenue, more than triple the opening weekend take for the latest Potter movie, “Harry Potter and the Order of the Phoenix,” which came out July 10.

“The excitement, anticipation, and just plain hysteria that came over the entire country this weekend was a bit like the Beatles’ first visit to the U.S.,” Scholastic president Lisa Holton said in a statement yesterday.

“This weekend kids and adults alike are sitting on buses, in the park, on airplanes, and in restaurants reading ‘Harry Potter and the Deathly Hallows.’ The conversations the readers have been waiting to have for 10 years have just begun.”

The numbers are astonishing, but not shocking. “Deathly Hallows” was designed to break records, released Saturday with a first printing of 12 million in America alone, although Scholastic spokeswoman Kyle Good acknowledged that some stores already were out of copies.

“Our distribution strategy was clearly right on target in order to sell 8.3 million copies in 24 hours,” she told the Associated Press. “We are working with retailers to move additional copies to the places they are needed most in the coming days and weeks.”

The book’s British publisher, Bloomsbury, expects to announce sales figures today.

Borders Group Inc. reported that “Harry Potter and the Deathly Hallows” sold 1.2 million copies worldwide in its first day, the biggest single-day number ever for the superstore chain.