The Harry Potter author announced her new online project in June. The website will allow fans to read the seven-book series while enjoying an interactive element, along with new information direct from Rowling.
While Pottermore will officially open in October, one million users will be granted early access to a beta version over the coming weeks.
The competition to win one of the places began yesterday, the day of Rowling and her title character's birthdays. Fans were asked to answer a cryptic question which would lead to them discovering 'The Magical Quill'.
Over a seven-day period, a certain number of fans each day will secure their place. However, those who do so will not be given immediate entry. From August 7, a 'welcome letter' will alert them to when they can begin using the website.
The Pottermore website today experienced heavy traffic as the second 'Magic Quill Quest' challenge began. A message confirmed that there was "overwhelming demand", while the page would refresh automatically in an attempt to gain entry.
Demand for early access was so high that one successfully registered user has already placed their account on eBay.
When announcing the project, Rowling confirmed that her best-selling series will be sold as e-Books on Pottermore from October.
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Watch JK Rowling's Pottermore announcement below: