May 22 (Reuters) – Shares of Chinese e-commerce firm JD.com Inc soared almost 20 percent in their U.S. market debut as investors sought a piece of the country’s booming online retail market, auguring well for Alibaba Group Holding Inc’s hotly anticipated mega-float later this year.

JD.com, China’s largest e-commerce company after larger rival Alibaba, was briefly valued at more than $30 billion before the stock pared its gains. By midday, the stock was up about 8 percent at $20.50, versus its $19 initial public offering price.