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 / Updated  / Source: Reuters

U.S. online sales surged on Black Friday, with Inc offering the steepest discounts among e-commerce sites as it set the agenda for what has traditionally been the biggest shopping day of the year for brick-and-mortar retailers.

In-store shopping began to pick up in the afternoon, but the increase in customer traffic paled in comparison to the jump in online sales, analysts said.

Macy's Inc website saw such heavy traffic that it had to delay customers from entering the site at three different times.

Related: Macy's Website Crashes After Black Friday Traffic Spike

Online sales on Friday hit $1.70 billion as of 3 p.m. EDT, according to Adobe Digital Index, after reaching $1.13 billion for the day on Thursday, up almost 14 percent from a year ago.

The National Retail Federation has said it expects total sales this holiday season to increase by 3.6 percent to $655.8 billion, mainly due to the rise in online shopping.

People enter Macy's Herald Square for early opening of the Black Friday sales in Manhattan, New York, on Nov. 24, 2016.ANDREW KELLY / Reuters

This weekend's shopping could reflect signs of faster economic growth in the fourth quarter this year. Nationwide U.S. retail sales rose 0.8 percent in October, driven by a 1.5 percent jump in receipts at online retailers.

The lowest unemployment rate in eight years of 4.9 percent in October and a rise in hourly wage rates of 2.8 percent for the year, the biggest increase since 2009, is fueling consumer confidence and spending power.

"All of this adds up to the consumer feeling better about their current situation and I'm hoping they ... buy all of their gifts from Macy's," the retailer's chief executive officer, Terry Lundgren, told Reuters.

Related: The Five Days of Black 'Friday': Election Behind Them, Consumers Spend, Spend, Spend

Administrative assistant Kelsey Gilford, 52, was shopping at Chicago's Water Tower mall on Friday but had already made purchases online on Thursday.

"I looked at some online deals on J.C. Penney which were good. I bought a small kitchen appliance yesterday," she said.

The deepest average discounts for Black Friday came from leading online retailer Inc, with an average of 42 percent off, compared with 33 percent off at Walmart , 35 percent at Target and 36 percent at Best Buy, according to e-commerce analytics firm Clavis Insight.

Amazon said Black Friday would surpass last year in terms of the number of items ordered on its website. The Seattle-based company declined to provide specifics.

Both Target and Wal-Mart, two of the country's biggest brick-and-mortar retailers, said Thanksgiving online sales were some of their best ever.

Related: Who Spent the Most on Black Friday? You Might Be Surprised

Customer traffic online could be up 20 percent over Black Friday from a year ago, Cowen & Co analysts forecast in a note, while store traffic is likely to fall 3 to 4 percent this year on Black Friday.

"We expect negative (store) traffic given (the) earlier start this year of the holiday selling season and rise of mobile, which could be as much as 60 percent or more of all traffic, and consumer exhaustion from a saturated promotional environment," the analysts said.