US retail sales figures in the critical Thanksgiving weekend rose 16% versus a year ago to $52.4bn, the National Retail Federation (NRF) has said. The figures include Black Friday, the first day after the Thanksgiving holiday, when stores reopen. NRF estimated that 86 million customers shopped online and in-store on Black Friday - the day traders traditionally leave the red and make a profit. Thanksgiving Day itself saw 29 million shoppers. According to research by ShopperTrak, provider of retail and mall foot-traffic counting services, Black Friday sales increased 6.6% over the same day last year. This is equal to $11.4bn in retail purchases, and the biggest dollar amount ever spent during the day. Retail foot-traffic rose accordingly, by 5.1% over Black Friday 2010. Analysts are awaiting the results of Monday\'s trading, known as Cyber Monday, which online retailers including Amazon cite as their biggest business day of the year. \'Largest increase since 2007\' US electrical retailer Best Buy was cited as a strong performer over the Thanksgiving weekend. Its strategy of opening stores at midnight on Thursday, and offering deals that could only be found in-store, forcing shoppers to step inside, was seen as a smart business move by analysts. Shoppertrak founder Bill Martin said: \"This is the largest year-over-year gain in ShopperTrak\'s national retail sales estimate for Black Friday since the 8.3% increase we saw between 2007 and 2006. \"Still, it\'s just one day. It remains to be seen whether consumers will sustain this behaviour through the holiday shopping season.\"