Singles Day began as a spoof event celebrated by unattached Chinese university students in the 1990s.
In Chinese, it is called "Double 11", after the numbers in the month and date.
The informal holiday was co-opted by e-retailers in 2009 and transformed into China's version of Cyber Monday, as the Monday after Thanksgiving is known.
About $9 billion in sales were made on Cyber Monday in 2017, up about 17 per cent from the previous year, according to Adobe Analytics.
Ren Xiaotong, a 27-year-old accountant in Beijing, said she suspected online stores jacked up their prices in the lead-up to Singles Day so they could declare that items were discounted.
But in the end, her scepticism did not stop her from partaking.
"Singles Day is different now — it has more tricks than before," she said.
"You only save a few dozens of yuan at the end. That being said, I still bought a pair of shoes, simply to celebrate the festival."
The Twitter-like Weibo platform was blanketed with Singles Day-related posts on Sunday, from users proudly proclaiming they had resisted the shopping urge this year to those who cheerfully listed an array of mundane purchases.
'A day of gratitude': Alibaba founder
Alibaba founder Jack Ma, who will step down as chairman in less than a year, attended the start of the gala in Shanghai and appeared in a video message in which he wrapped up live hair crabs, a popular online purchase.
Singles Day "is not a day of discounts, but rather a day of gratitude", he said in the video.
"It's when retailers use the best products and best prices to show their gratitude to our consumers."
Chinese e-commerce platforms have come under fire in the past for peddling low-quality and counterfeit items.
Hong Tao, an economics professor at Beijing Technology and Business University, said Singles Day encouraged shoppers to prioritise cheap prices over high quality, causing them to purchase items they do not need.
"People are swept up in the festivities," Professor Hong said in a phone interview.
"This burst of consumption, confined to just one day, can be exhausting for both buyers and sellers."
(Source: ABC/wires)