Major e-tailers such as Flipkart and Amazon are likely to achieve total sales of $2.5 billion to $3 billion during the five festive days of October, according to a report by research and advisory firm RedSeer Consulting.

The Bengaluru-based firm said this year the e-tailers can expect over 20 million shoppers in the five-day sale, which will be highest in last two years. In 2016, 10 million shoppers flocked online sites for festive purchases while last year, the number was between 13 to 14 million.

In terms of what the shoppers will buy, the report said, the trend is likely to be similar to the last two years.

Mobiles and tablets are expected to take up nearly 52 percent of the customers' shopping list this year while other electronic items and fashion will make up for 23 percent and 15 percent, respectively.

"We expect the large AOV (average order value) items like electronics and furniture share to increase this festive season due to 'affordability' initiatives," said the report.

The RedSeer report expects the major e-tailers to see a near 60-70 percent rise in shipments to 48 million this year.