NEW YORK - Shoppers' visits to physical stores across the United States this Thanksgiving holiday season were not as robust as last year, according to a report on Saturday.

Preliminary shopper visit for brick-and-mortar retail stores and shopping centers on Thanksgiving Day and Black Friday declined 1 percent from last year, said ShopperTrak, a retail tracking firm, in a statement.

The data also indicated a 1.7 percent decline in traffic on Black Friday as compared with that in 2017.

The popularity of online shopping was part of the reason for the dip, analysts noted.

"We know that online sales ... have certainly eroded traffic from retailers over the years," said Brian Field, senior director of advisory services for ShopperTrak, adding that Black Friday is still expected to be the busiest shopping day of the year, according to CNBC.

Black Friday, the day after Thanksgiving that marks the official start of the US holiday shopping season, pulled in $6.22 billion in online sales this year, up 23.6 percent from a year ago and setting a new high, according to Adobe Analytics, which tracks transactions for 80 of the top 100 internet retailers in the United States, including Walmart and Amazon.

Despite the pullback, Field said that shopping in physical stores during the holidays continues to be an exciting annual event for consumers.

"Providing an unparalleled customer experience throughout the shopper journey makes the season festive and fun and will bring shoppers back well beyond the holidays," Field said in ShopperTrak's Saturday statement.

The retail tracking firm also predicted several busy shopping days to come this year, including Super Saturday, which will fall on Dec 22, and the Sunday before Christmas, Dec 23.

A recent survey by the National Retail Federation (NRF) showed that an estimated 164 million people across the United States plan to go shopping from Thanksgiving Day to Cyber Monday.

Holiday retail sales in November and December will be up between 4.3 percent and 4.8 percent over 2017 for a total between $717.45 billion and $720.89, according to projections by NRF.