U.S. retailers have begun their "Black Friday" sales, reopening stores after the Thanksgiving holiday, BBC News reported.

Black Friday is usually the busiest shopping day of the year, as the Thanksgiving weekend marks the start of the holiday shopping season.

A survey estimated that 147 million people would go shopping between Friday, November 23 and Sunday, despite more shoppers going online.

With the U.S. economy fragile, many shops began their sales on Thursday night.

Retailer Target opened its doors at 9pm local time, three hours earlier than last year. Sears opened at 8pm. When department store Macy's opened its flagship in New York at midnight, 11,000 shoppers arrived.

The National Retail Federation forecast a 4.1% increase in retail sales during the November-December holiday period this year, less than the 5.6% jump recorded last year.

And the 147 million people forecast for this year is down from 152 million on the Thanksgiving weekend last year, the NRF said.

More than 50% of consumers will do some browsing during the weekend, according to Kevin Sterneckert, vice president of retail research at Gartner.