LONDON J.K. Rowling couldn't find the exact word to describe her reaction as her latest Harry Potter book went on sale Saturday.

"I'm amazed-think of a stronger word and double it," Rowling said at King's Cross Station, where she launched the book in England.

Parents scuffled and children wept as Rowling was greeted more like a film star than a writer. She described the pandemonium surrounding her latest book as "complete madness."

Across Britain and the United States, parents and children stayed up into the early-morning hours Saturday to get the 734-page book, Harry Potter and the Goblet of Fire. It's twice as long as previous Harry Potter stories.

"It was the hardest so far to write. It's a long book," Rowling said. "It's the culmination of 10 years' work. There was a lot of external pressure this time.

"I knew it was going to be longer than the third, but I was surprised at how long it was. That's how long it needed to be to tell the story."

Rowling, a single mother from Edinburgh, Scotland, knew she had shattered the record for advance orders with 5 million globally even before she embarked on the nationwide publicity tour to promote the latest adventure of her hero, a bespectacled teenage wizard.

Before leaving King's Cross' Platform 1-transformed into Platform 9 3/4 in honor of Harry Potter's gateway to his mystical world-her fourth book was selling at the rate of up to 350 an hour in large bookshops in Britain.

The hoopla Saturday was "certainly not anything I ever expected, far from it. I never dreamed of this," Rowling said.

At Waterstone's in Piccadilly, 1,200 copies of the book were snapped up before lunchtime.

"It's huge. It's the fastest-selling children's book I've ever known. The kids just couldn't wait to get their hands on it," said Becky Thomas, assistant manager at W.H. Smith.