Chinese retailer Alibaba on Monday said sales for its annual Singles' Day shopping blitz jumped 25% in the first nine hours to $23 billion, nearly two-thirds of US rival Amazon.com Inc's online store sales in the latest quarter.

Sales growth for the full 24-hour event, however, is likely to fall short of the year earlier, analysts said, at a time when China's economic expansion heads toward a historic low.

The event, a gauge of Chinese consumer sentiment, has also become a shop window this year for Alibaba Group Holding Ltd as the firm plans to sell $15 billion worth of shares in Hong Kong. US-listed Alibaba has spent big to diversify its business yet still earns over fourth-fifths of revenue from e-commerce.

Akin to Black Friday and Cyber Monday in the United States, Singles' Day has been promoted as a shopping fest by Alibaba Chairman and Chief Executive Daniel Zhang since 2009, and has grown to become the world's biggest online sales event.

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Also known as "Double Eleven", the festival's name originates from the calendar date Nov. 11, with the four ones of 11/11 signifying being single.

What started as a marketing gimmick has been replicated by rivals at home and abroad. As well as longtime competitor JD.com Inc, Singles' Day promotions can be found at China's Pinduoduo Inc as well as South Korea's 11thStreet and Singapore's Qoo10.

Slowing online sales growth has prompted Alibaba to expand in less-developed areas outside of China's massive first- and second-tier cities.

"The younger generation is buying more, and the customer from the rural areas, the customers from lower-tier cities, they are buying imported products," Alvin Liu, general manager of Alibaba's Tmall, told a media panel.

Alibaba netted online sales worth $30 billion across its platforms on Singles' Day last year, dwarfing Cyber Monday's $7.9 billion. The figure was 27% higher than the year earlier yet it was the lowest in the event's 10-year history.

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A sign of Alibaba Group is seen during the fourth World Internet Conference in Wuzhen, Zhejiang province, China, December 3, 2017.REUTERS/Aly Song/File Photo

For this year, Citic Securities forecast Singles' Day sales growth of 20-25%, held back partly by slowing overall e-commerce growth in China.

The Chinese retail juggernaut, with a market value of $486 billion, kicked off this year's 24-hour shopping fest with a live performance by U.S. pop star Taylor Swift followed by live-streamed marketing of over 1,000 brands.

Alibaba said sales hit $1 billion in the first minute and eight seconds and reached 158.31 billion yuan ($22.6 billion) in the first nine hours, up 25% from the same point last year.

Alibaba has said it expects over 500 million users to make purchases this year, about 100 million more than last year.

This is the first time Alibaba's Singles' Day does not have flamboyant co-founder Jack Ma at its helm, after he resigned in September as chairman to "start a new life".