YAHOO! Inc will buy 10 percent of the shares to be sold in the Hong Kong initial public offering of Alibaba.com Ltd, the business-to-business unit of China's largest e-commerce company, according to a preliminary document.

Alibaba.com Ltd and parent Alibaba.com Corp will offer a combined 858.9 million shares, or a 17 percent stake in the former, in the share sale, according to the document.

Alibaba.com's IPO may raise US$1 billion, people familiar with the situation said earlier. The share sale would be the largest IPO by a Chinese Internet company, according to data compiled by Bloomberg News.

About 73.5 percent of the shares on offer will be sold by Alibaba.com Corp, the document said. The rest are new shares to be issued by Alibaba.com Ltd.