The U.S. holiday shopping season has arrived. Across the country, Americans are swarming retail stores in a yearly frenzy known as “Black Friday.”

At malls and stores from Los Angeles to New York, crowds of people stood in lines for hours waiting to get their hands on high-priced items specially discounted for the day. Some 11,000 shoppers had surrounded Macy's flagship department store in New York City's Herald Square when it opened at midnight.

“Things are going well. I got here at midnight, actually here about 11:30 and opened the doors, and we had record crowds here at Macy's Herald Square. We guesstimated that it was 11,000 people, but I stood at the front door for 18 minutes, and the lines never stopped coming in, so it could be more than that, so, so far so good.”

Black Friday — the day after America's Thanksgiving holiday — is traditionally the year's busiest shopping day.

But what used to be just one day of shopping is now expanding. “Gray Thursday,” a trend that began last year, now has some stores offering a Thursday night start to the post-Thanksgiving shopping rush.

Many businesses are also taking part in “Cyber Monday,” a day of big online shopping deals.

The name “Black Friday” signifies retailers' expectations of high sales, as profits were once recorded in account books in black ink, while losses were recorded in red.

Consumer spending accounts for about 70 percent of the U.S. economy. Some retailers say end-of-the-year holiday spending accounts for about a quarter of their annual sales.

But this year, holiday sales are expected to increase by a smaller amount than they did last year.

At fault is the struggling U.S. economy, with more than 12 million workers still unemployed in the aftermath of the recession in 2008 and 2009. Many Americans are also concerned about the so-called “fiscal cliff” — more than $600 billion in automatic tax increases and spending cuts that go into effect January 1, unless President Barack Obama and Congress can reach a budget agreement.

The new expanded post-Thanksgiving sale hours are seen as a way to make shopping more convenient for Americans and encourage them to spend more.

In the past, retailers were usually closed on Thanksgiving, known for its family gatherings and turkey feasts.

Employees of some chain stores have circulated online petitions pleading with the public to “save Thanksgiving” and stop the Thursday openings so that employees can enjoy their Thanksgiving holiday.