Cyber Monday, when retailers offer hot deals online following the Thanksgiving holiday weekend, marked the biggest online spending day ever, data showed on Wednesday.
According to research firm comScore, Web sales reached 1.03 billion dollars on Monday, up 16 percent from last year and topping the one billion dollar threshold for the first time in US history.
Monday's sales represent "the heaviest online spending day in history and the first to surpass the billion-dollar threshold," it said in a statement.
Online sales for the Thanksgiving weekend, from last Thursday to Sunday -- including Black Friday, which is traditionally considered the biggest shopping day of the year -- totaled 2.97 billion dollars, comScore said.
"The online holiday shopping season has clearly gotten off to a very strong start, which is welcome news," said comScore chairman Gian Fulgoni.
At the same time, he said, the strong sales are "almost certainly the result of retailers heavier-than-normal promotional and discounting activity at this early point in the season."
Retailers and investors are hoping to see robust sales this holiday season, but Americans were likely to spend cautiously amid high unemployment and a tepid economic recovery.
Many traditional brick-and-mortar retailers have jumped on the online shopping wagon in recent years, with giants such as Wal-Mart, Nordstrom and Macy's all reporting sharp increases in recent Internet sales activity.
Explore further: Is big data still big news?