"It's a recognition that retailers need to be more aggressive and want to show their physical stores are important," Moody's senior analyst Charles O'Shea said.

While he didn't see enormous crowds out in Vauxhall, New Jersey, he did see about 15 people lined up already at a Best Buy, which opened at midnight. At another Target, only two shoppers were in line for a 9pm opening. Still, for retailers, any crowd could make the effort worth it.

"It's a finite pie; if you can get a bit more by being open, then do it," O'Shea said.

The National Retail Federation, an industry trade group, forecast a 4.1 per cent increase in retail sales during the November-December holiday period this year, down from the 5.6 per cent increase seen in 2011. Some retailers, like Best Buy are keeping Black Friday on Friday, waiting until midnight to open.

At a Best Buy in Orlando, people camped out in tents for days waiting for the doors to open.

Gabriel Esteves, 33, a self-employed car audio installer, waited in line with a bag of Cheetos and a Coke while his brother and sister went to their homes for Thanksgiving feasts with their families.

"They told me to take a break and go to the house, but today's the worst day to leave the line. People come and cut in line," said Esteves, who got in line on Monday to buy some small electronics and a 50-inch television.

Best Buy, which is trying to stem falling sales under new chief executive Hubert Joly, is one of the retailers in the spotlight this season.

At some stores, workers were not so happy to have early openings encroach on their Thanksgiving holiday. A petition asking Target to "save Thanksgiving" had 371,606 supporters as of Thursday afternoon.

Still, at a Target on Chicago's northwest side, the first person waiting in line on Thursday night was someone who worked at the store, Elsa Acevedo, 46, who finished her shift at 4.30am and lined up at about 2.30pm to buy a 50-inch Westinghouse television.

As for the earlier opening, "I just think it takes people away from their families," she said. But she added that a midnight opening also pulled workers away from Thanksgiving celebrations because they had to prepare the stores to open.

Many shoppers lured into stores by earlier openings on Thursday may just be window-shopping.

More than half of consumers would do some form of "show-rooming" during the Black Friday weekend, said Kevin Sterneckert, vice-president of retail research at Gartner Group.

"They will buy things because they looked at it in the store. They will touch and feel what they are interested in and then buy it online on Monday, either from the same retailer or a different online retailer," Sterneckert said.

At a Kmart on 34th Street in Manhattan earlier on Thursday, Charles Montague, a 55-year-old mover, was browsing the aisles just to kill time.

"I don't holiday shop," he said emphatically. "I buy stuff all year long, not during some man-made holiday."

Some were not waiting for Monday to buy on the internet. Online Thanksgiving 2012 sales were already up 17.8 per cent over last year's figures, measured up to 9pm on the US east coast, according to IBM.

The stakes are high for US retailers, which can earn more than a third of their annual sales in the holiday season.

US consumers heading into the holiday shopping season remain worried about high unemployment and possible tax increases and government spending cuts next year.

Also, lasting effects of Sandy, the storm that lashed the densely populated east coast in late October, could cut into holiday spending.

According to a Reuters/Ipsos poll, two-thirds of shoppers said they planned to spend the same amount as last year or were unsure about spending plans, while 21 per cent intended to spend less and 11 per cent planned to spend more.