Cyber Monday sales were on pace to hit $6.59 billion by the end of the day, Adobe Insights revealed Monday evening.

That projection, made by the firm at 10 p.m. ET, would represent an increase of 16.8 percent when compared with the same time last year, Adobe found.

The firm measures 80 percent of online transactions from 100 major U.S. retailers.

Adobe had originally forecast total online spending on Monday to surpass $6.5 billion, which would have been enough to make the cyber holiday the largest digital shopping day in U.S. history.

A record $5.03 billion was spent online during Black Friday, an increase of 17 percent when compared with last year, Adobe found. Top-selling items that day included the Nintendo Switch, Hatchimals, L.O.L. Surprise and ride-on cars for kids.

On Monday, more toys, handheld electronics and apparel merchandise led the way with heavy discounting.

Meanwhile, Small Business Saturday and Sunday delivered a combined $5.12 billion in online sales, up 10 percent from a year ago, Adobe added.

Driving clicks and sales overall this holiday season have been smartphones and other mobile devices, as purchases made from desktop computers haven't been as strong.

"People are really figuring out how to use their mobile devices," Mickey Mericle, vice president of Adobe's Marketing and Insights division, told CNBC's "Squawk Alley" Monday afternoon.

"And retailers are figuring out how to optimize ... for mobile," she added. "We're seeing the two come together."