Is Black Friday gone for good?

Once the biggest and most famous shopping day of the year, more and more retailers are now extending sale periods and offering bonus deals online.

The big discounts might no longer be just about the day after Thanksgiving, but is Black Friday really a thing of the past?

According to the National Retail Federation (NRF), in the U.S. an estimated 135.8 million shoppers are likely to shop on Thanksgiving, Black Friday and over the weekend. Up from last year's Thanksgiving weekend as the shift moves away from Friday as the key shopping day.

NRF President and CEO Matthew Shay said he expected retailers to also offer exclusive savings and promotions throughout the week that follows the Thanksgiving weekend and Cyber Monday.

"This weekend isn't the end-all-be-all; it's important to remember, there will be several important weekends to keep an eye on before we wrap up the holiday season," he said in a statement.

Amazon.com (NASDAQ: AMZN), the world's largest online retailer, announced on Tuesday it will extend its holiday savings for an additional eight straight days of new deals. It said new price cuts will be added as often as every five minutes as a "celebration" of Cyber Monday.

The online giant is offering some of its best "lightning" deals on the Amazon smartphone or tablet app, or customers can sign up for mobile alerts to find out when new specials are offered.

"We could be looking at a Red Friday rather than a Black Friday. Retailers are becoming dazed and confused as they are being pulled in every direction trying to outdo each other with the most competitive offers and looking to delivery orders faster than the competition," said Siobhan Gehin, head of strategy and private equity at global consultancy firm Kurt Salmon.

"In reality this situation is just eating into retailers' profits and is not sustainable."

Meanwhile, Wal-Mart (NYSE: WMT) is moving "Cyber Monday" to Sunday because people now have fast Internet in their homes, the U.S. retailer said Monday.

All 2,000 of Wal-Mart's Cyber Monday deals will begin Sunday at 8 p.m. ET.

"By starting Cyber Monday hours earlier on Sunday evening and quadrupling the number of Cyber Monday specials, we're making it easier for customers to get ahead of the busiest online shopping day of the year and save on the best gifts," Fernando Madeira, president and chief executive of Walmart.com, said in a press release.

Other major U.S. retailers including Target (NYSE: TGT) said they will offer the same deals online as in store from Thanksgiving morning.

Meanwhile, across the Atlantic in the U.K., catalogue and warehouse retailer Argos said its decision to begin Black Friday discounts long before November 27 has paid off with the site achieving a 22 percent rise in traffic, according to digital analytics firm SimilarWeb.

The retailer was one of the first to start its Black Friday sales a week ahead of Black Friday, with deals between November 20 and 22.

But as Black Friday is still a relatively new event in the U.K., analysts are still predicting bumper spending on the day, even as retailers extend the time period for discounts.

U.K. consumers are expected to spend more than £1 billion ($1.5 billion) online on Black Friday this year. The U.S. imported phenomenon really took off back in 2013, when sales jumped 20.7 percent compared to the year prior, according to Barclaycard data.

"Reports of the death of Black Friday are exaggerated and it appears this year's will be bigger than ever. Nearly half of those who didn't shop last time are considering it for November 27th and the majority of sales will be online," said Ian Hughes, the chief executive of Consumer Intelligence said in a stament.

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