After a day on sale, forecasters say '25' could sell at least 2.5 million in its first week in the U.S.

After one day on sale, Adele's 25 appears set to break *NSYNC's long-standing one-week Nielsen-era U.S. album sales record of 2.42 million sold, according to industry forecasters. Sources say the set is on track to sell at least 2.5 million in pure album sales in its first week, and sold more than 900,000 copies alone through the iTunes Store on its first day of release.

The 10 Most Heartbreaking Lyrics From Adele's '25'

25 was released on Nov. 20 through XL/Columbia Records. It's Adele's third studio album.

*NSYNC currently owns the single largest sales week for an album since Nielsen Music began tracking point-of-sale music purchases in 1991. (Prior to 1991, there was no authoritative music sales tracking service in the U.S. and thus, it was mostly unknown how many copies of an album or song/single were sold in a single week.)

*NSYNC's No Strings Attached debuted with 2,416,000 sold in the week ending March 26, 2000. No Strings Attached has since remained the only album to sell 2 million copies in the U.S. in a single week.

Adele's '25' Won't Be On Streaming Services

Nielsen Music's tracking week runs Friday through Thursday each week, so 25's first week will conclude on Nov. 26. Billboard is scheduled to report 25's debut week sales on Nov. 29, once Nielsen has finished processing its weekly data.

Before 25's release, it was reported that the album shipped 3.6 million physical copies to retailers. In addition, sources were forecasting 25's CD configuration to sell 1.5 million in its first week, while its digital edition could move another 1 million (meaning, its first week might be at least 2.5 million in total).

Now perhaps the question is: How much bigger can 25 get? Will it blow past the 2.5 million threshold? Can it hit 3 million? And what will 25 sell in its second and third week? Could it become the first album to sell a million copies in more than one week?

Adele Powers Through Lifetime of Regret on '25': Album Review

If 25 sells as expected, it will become the 20th album to sell at least a million copies in a single week in the Nielsen era. It would also instantly be the largest selling album of 2015 in total, surpassing the sales of Taylor Swift's 1989, which has sold 1.74 million this year (through Nov. 12).

25 is also on course to debut at No. 1 on the Billboard 200 albums chart (dated Dec. 12), which would give the diva her second No. 1. She first led the list with her last album, 21, which spent 24 nonconsecutive weeks atop the list -- most weeks at No. 1 for an album by a woman. 21 has sold 11.23 million copies in the U.S., and is the tenth-largest selling album of the Nielsen era.