Braving rain that made it almost impossible to sleep, the fans took shelter under large umbrellas to mark their spot in Trafalgar Square, where the stars of the movie will make a red-carpet appearance for "Harry Potter and the Deathly Hallows: Part 2."
Groups of girls screamed with excitement as they painted each others' faces in the red-and-yellow colours of Gryffindor, one of the four houses of the wizarding Hogwarts school in the Harry Potter books. Harry's house, of course.
"It's amazing," said Lydia Jenkins, 16, a schoolgirl from London. "There's so much anticipation."
Sporting clothing like that worn by imaginary wizards from the Hogwarts house Hufflepuff, 47-year-old Paul Taylor said he was hoping to get autographs from the film's stars.
"I've been to quite a few of the premieres before, but I've never managed to get any autographs, so hopefully today I'll do that," he said.
Some fans travelled thousands of miles for the event. A group of Mexican fans held aloft their national flag and a banner praising J.K. Rowling the author who brought the bespectacled Harry and his world of wizards to life in her books.
Sydney Bogatz was among a group of Americans from Las Vegas who were camped patiently on the pavement outside the square.
"It's really exciting. It's my first premiere," the 18-year-old said. "I'm a longtime Harry Potter fan and I'm really excited to see Rupert Grint walk on the red carpet." Grint plays Ron Weasley, Harry's pal.