Black Friday is Underway Across the United States

(AP)-- UNDATED-- The shoppers are coming in waves after some retailers opened their doors for Black Friday on Thanksgiving.

A spokeswoman at Mall of America in Minneapolis says 30,000 people showed up for the mall's midnight opening -- compared with 20,000 last year. Julie Hansen says stores that didn't participate in the midnight opening last year learned a lesson.

About 11,000 shoppers lined up around Macy's in New York City when it opened at midnight. That's up from an estimated 9,000 to 10,000 shoppers who showed up for the store's midnight opening last year.

Some of the stores that opened on Thanksgiving were Target and Toys R Us.

The earlier hours are an effort by stores to make shopping as convenient as possible for Americans, fearing they won't spend as freely during the holiday season because of economic uncertainty.

There's added pressure on brick-and-mortar stores as more Americans shop on websites that offer cheap prices and the convenience of being able to buy something from smartphones, laptops and tablet computers.

The National Retail Federation estimates overall sales in November and December will rise 4.1 percent this year to over $586 billion. But according to Forrester Research, the online part is expected to rise 15 percent to over $68 billion.