The launch of the first books in Mind Candy's Moshi Monsters franchise attracted huge crowds at the Westfield branch of WH Smith at the weekend, with some fans queuing for more than four hours to get their hands on a copy.
The Moshling Collector's Guide (£6.99) and My Moshi Monsters Joke Book (£4.99) were being signed by Michael Acton Smith, chief executive of Mind Candy.
The first 150 children in the queue were treated to special goodie bags, with other attractions including face painting and balloon modelling. Two full-sized Monsters - Poppet and Furi - were also on hand.
"The response from fans has been unbelievable and copies of the book have been flying off the shelves," Acton Smith said. "To think that some kids were queuing hours before the store opened shows just how popular Moshi Monsters has become."
A WH Smith spokesperson added: "The book launch with Moshi Monsters was a fantastic occasion; we are thrilled to be working with Sunbird and Mind Candy on this event. The response from the hundreds of children in attendance was absolutely amazing."
Moshi Monsters now has over 29 million players across the world. The site allows children to adopt their own free pet monster, play games, customise their homes, explore the virtual world and solve puzzles.