Samsung S, the first device of the smartphone series, had taken seven months to achieve the same numbers.
South Korean Chosun Ilbo daily published the figures citing sources from Samsung, who refused to confirm or deny the figures to EFE news on Wednesday.
The new models of the Galaxy S series went on sale on April 21 in South Korea, Canada and the US and subsequently in other markets, including Europe, and will be launched in China on Thursday.
The company is planning to launch the smartphone in around 120 countries by the end of May.
According to analysts, given its current success, the S8 could end up surpassing the 50 million units its predecessor – the Galaxy S7 – sold.
Meanwhile, pre-orders for Galaxy S8 exceeded one million in South Korea, where 260,000 units were sold on the first day of its release, according to the report.