SHANGHAI — After 24 hours of frenzied buying and selling, and weeks of advertising and promotions before it, the Alibaba Group announced that its sales hit another titanic high on Singles Day, the Nov. 11 shopping festival that the Chinese e-commerce behemoth cooked up a decade ago.

This time, as China’s vast economy slows, the party was held with icebergs in sight from the deck.

China’s biggest online shopping company kicked off the country’s biggest shopping day with its usual ostentation. Its Saturday night gala event in Shanghai featured the singer Mariah Carey, the retired basketball star Allen Iverson and Miranda Kerr, the Australian supermodel. A Chinese girl group performed a song called “Wanna Buy Wanna Buy” as backup dancers pushed shopping carts bearing the logo of Aldi, the German discount grocer.

At the stroke of midnight on Monday, Alibaba said it had racked up $30.8 billion in sales the day before, as measured by its own metric, gross merchandise value. That handily topped last year’s big number, $25.3 billion.

But all around China, gloom and uncertainty are the word.

Economic growth is slowing, and the country’s hundreds of millions of middle-class shoppers seem to be holding on more tightly to their pocketbooks. Tech companies are antsy about the government’s more interventionist attitude toward big business. The tariff fight with the United States is casting a pall not simply over trade, but over China’s future writ large. This month, Alibaba cut its sales forecast for the year ending in March by around 5 percent, citing the wobbly economy and the trade war.