Workers distribute express parcels at a logistics centre of China Post during Alibaba Group's Singles' Day global shopping festival on November 11, 2016 in Ganyu, China.

Chinese e-commerce giant Alibaba promises that this year's annual Singles' Day this Sunday will be the "largest-ever in terms of scale and reach."

The holiday, which started as a day for unmarried Chinese to buy gifts for themselves, has become the biggest single shopping event in the world. Consumers bought a record $25.3 billion in merchandise during last year's Singles' Day — surpassing the $19.62 billion spent between Thanksgiving and Cyber Monday in 2017.

Amazon said it sold more than 100 million items during its Prime shopping holiday on July 16, with analysts estimating that consumers spent about $4 billion, by comparison.

"If you take Prime Day which happened this summer, Amazon reported $4 billion this year which is a really strong number but in comparison it's kind of cute," said Danielle Levitas, executive vice president of market insights at App Annie, which provides mobile data and insights.

According to Levitas, App Annie is projecting that Singles' Day will drive $32 billion in spending this year.

Alibaba is pushing a new strategy this year, promoting sales both online and in brick-and-mortar stores.

"One of the reasons the 180,000 merchants and 600 million consumers in China and consumers outside of China are so interested in this Singles' Day event is because it gives them many, many more opportunities to participate, and to be involved in something that is both fun but also a great experience," Alibaba President Michael Evans said on CNBC's "Squawk on the Street" on Friday.

In the past few years, Singles' Day has surpassed the transaction volume of both Black Friday and Cyber Monday combined. The event has also far surpassed Amazon's Prime Day, which is the most similar to Singles' Day because it is also a 24-hour, online shopping event.

China's middle class is significantly bigger than the total U.S. population and the country is more technologically savvy, Levitas said.

"You combine the size of the population, their sophistication, acceptance, and preference for mobile and it's not surprising that the U.S. and something like Prime Day's success will be substantially smaller," she said.

According to Levitas, Americans spent an estimated $8 billion on Black Friday both in physical stores and online, and Cyber Monday raked in about $6.6 billion.