Some cite demographics and timing: University graduates who adopted the holiday earn more and shop online. Singles Day comes as people receive monthly paychecks and need to buy winter clothes. Unlike other events such as the Lunar New Year, China’s biggest family holiday, it involves few other expenses such as travel or banquets, leaving more money for gifts.

And there is the romantic angle that might prompt shoppers to open their wallets.

‘‘This is about giving a gift that will woo that perfect someone,’’ Natkin said. ‘‘If you play your cards right, you only need to make that purchase once.’’

Lei, the Shanghai designer, wound up buying only the pillow from her shopping list for 118 yuan ($18) because other discounts weren’t as big as she hoped.

‘‘I will wait to see if I can get them later,’’ she said.

Companies began preparing for Sunday months in advance.

At its headquarters in Hangzhou, southwest of Shanghai, Alibaba set up 200 lounge chairs for its 800-strong staff to rest during the day. The company rented 180 rooms at nearby hotels for longer breaks.

On Tmall.com, called Tian Mao, or ‘‘Sky Cat,’’ in Chinese, goods ranged from clothes, books and furniture to discounts on restaurant meals and travel packages. An auto dealer in the southern city of Shangrao offered 23 percent off BMW 3-series luxury cars ordered Sunday.

China’s delivery companies had 800,000 employees working Sunday, including 65,000 temporary workers hired for the holiday, the China Daily newspaper said, citing the country’s delivery industry association.

One of the biggest, YTO Express Co. Ltd. in Shanghai, planned to have 30,000 vehicles on the road, the newspaper said, and expanded its daily handling capacity by 50 percent to 6 million packages for the day.

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