New Delhi, Oct. 15: E-commerce giants such as Amazon, Flipkart and Snapdeal are dealing out deep discounts through flash sales and exchange offers to attract shoppers who are expected to shell out Rs 40,000 crore to shop online during Durga Puja and Diwali, according to industry estimates.

Flipkart today said it had sold 5,00,000 mobile handsets in the last 10 hours as part of its "Big Billion Days" sale. The deep discounted sale of mobile phones started on midnight of October 14.

The Big Billion Days festive sale started on October 13 and will end on October 17.

"It has been a blockbuster beginning for our mobile category. Half a million mobile handsets sale record is truly a testament to the growing demand for smartphones in India," said Mukesh Bansal, head of the commerce platform at Flipkart.

The Bangalore-based company said the platform saw a huge sale of 4G-enabled devices. "Seventy five per cent of the phones sold in 10 hours were 4G phones," Bansal said.

On the first day of the sale, it sold 10 lakh products in the first 10 hours with six million visits from across the nation and 25 items sold per second.

Amazon India has also launched The Great Indian Festival Sale during the same time as Flipkart's.

The US-based e-tailer has already witnessed double the sale of its previous biggest day - on Independence Day - when the company ran The Great Indian Freedom Sale.

Snapdeal, which had started offering deep discounts from last week, claimed that as part of its "Preview Monday Sale" sales revenue have increased 10 times and volumes are up six times across product categories compared with usual days.