The most sought-after tickets were football, beach volleyball, basketball, tennis and athletics, according to Rio2016.com on Thursday, reports Xinhua.
Officials said many of the tickets only became available in recent days, having previously been set aside for broadcasters.
Rio 2016 ticketing director Donavan Ferreti said tickets were still on sale for the men's 100m final, beach volleyball, marathon and football.
"We are very pleased with the rush for Olympic tickets experienced today," Ferreti said in a statement.
"We know that Brazilians are last-minute buyers and it is fantastic to see that the excitement and anticipation for the Games is now reaching its peak."
The Olympic Games will be staged in Rio de Janeiro from August 5 to 21.