American consumers arrived en masse in stores - and online - for the annual Black Friday shopping extravaganza that opens the US holiday shopping season.

Held the day after Thanksgiving, a period when schools are out and many offices are closed, Black Friday has evolved over the years into a massive shopping occasion known for "doorbuster" sales and other promotions to lure consumers into stores.

Retailers have also added a plethora of discounts online starting on Thanksgiving Day, accelerating on Black Friday and culminating on "Cyber Monday" just after the weekend. That has inevitably dented some of the consumer traffic at brick-and-mortar stores, although tens of millions were still expected to brave the crowds.