US retail sales on Black Friday hit a new record for the start of the holiday shopping season that follows Thanksgiving, according to early estimates published Saturday. Sales hit $11.4 billion, up 6.6 percent compared to last year, and the biggest dollar amount ever spent on Black Friday, Chicago-based research firm ShopperTrak said in a statement. It was the largest year-on-year gain since an 8.3 percent increase in sales between 2006 and 2007, the firm said. Foot traffic in stores was up 5.1 percent compared to Black Friday 2010. "Black Friday is the biggest shopping day of the year and the traditional start to the holiday shopping season," said ShopperTrak founder Bill Martin. "Despite our sluggish economy, shoppers proved they are looking for value and ready to buy if given a good customer experience." But the company warned: "Still, it's just one day. It remains to be seen whether consumers will sustain this behavior through the holiday shopping season." Shoppers mobbed malls and went online in droves to snap up bargains late Thursday, through the night and into Friday -- an annual sales ritual that marks the start to the end-of-year shopping season relied on by many retailers. The shopping frenzy lasts throughout the weekend and into Cyber Monday, when retailers offer hot deals online following the Thanksgiving holiday weekend. The increase in sales appeared to be far higher than the inflation rate, which eased to 3.5 percent in October as compared with a year ago, according to US Labor Department data. The National Retail Federation was due to publish its first Black Friday sales estimates on Sunday.