Around 400,000 people tried to log onto the web site simultaneously at 10 a.m., when ticket sales began, overwhelming it and causing it to crash, organizers said.
Two hours later the web site was finally "stabilized" and about 20 sales per second were being made.
A total of 595,000 tickets have been offered for sale for the seven-day festival, which runs from Sep 13-15 and 19-22, and - of those - 140,000 were sold at the pre-sale last October when organizers still did not know which bands were going to perform.
Rock in Rio this year will feature mega-stars like Bruce Springsteen, Beyonce, Metallica, Iron Maiden, Muse, Bon Jovi and Justin Timberlake.
Ticket sales are being made exclusively online, a decision by organizers to avoid the tremendously long lines of ticket buyers that resulted for the 2011 event.
Tickets cost 230 reais (USD 115) per day, with 50 percent discounts for retirees and Brazilian students.
Buyers who live abroad must pay an additional 52 reais (USD 26) delivery charge.
--IANS (Posted on 05-04-2013)