Black Friday has been quieter in the US this year, as customers flocked on e-commerce portals, and retailing giant Walmart's shops across the nation faced protests by thousands of employees over low wages.

In addition, retailers were open on Thanksgiving Day, generating significant sales and reducing traffic on Black Friday, which has been the busiest US shopping day in terms of sales and traffic since 2005.

Meanwhile, online sales jumped during the day, rising 8% year on year through late afternoon. The improvement was driven by increased use of mobile phones and tablets, which accounted for 6% of all Black Friday online traffic.

The Black Friday surge in online sales comes after a 14.3% increase in online sales on Thanksgiving Day, according to IBM Digital Analytics.

Walmart's e-commerce website crossed more than 500 million page views on Black Friday, the second highest for the firm after the Cyber Monday traffic in 2013. E-tailer Amazon's sales increased 26% from last year, while electronics retailer Best Buy's website went offline due to a surge in traffic especially from mobile devices.

Meanwhile, thousands of Walmart employees across the US protested against the company over low wages among other reasons. The protesters descended on some Walmart stores in Washington, New Jersey, Illinois and many other states, in what is being touted as the biggest organised protest against the retailer in its history.

There are more than 4,000 Walmart stores across the US, and the company employs about 1.3 million workers in the country, being the largest private employer.

Walmart said the demonstrations did not represent the view of its huge employee base, and the crowds were mostly made up of paid union demonstrators.