Alibaba IPO biggest ever; shares decline

Alibaba Group has reportedly sold additional shares of the company, making the listing of the Chinese e-commerce firm the biggest in history.

Alibaba shares opened lower in early trading Monday and tumbled more than 4 percent later in the morning. (Get the latest quote here.)

Reuters reported on Monday, citing sources who have direct knowledge of the deal, that bankers of Alibaba have exercised a "green shoe" option by buying an additional 48 million shares from the company to cover stock they sold to meet high investor demand.

This takes the value of the deal to $25 billion, exceeding the $22.1 billion IPO by Agricultural Bank of China in 2010 and the $22 billion listing by ICBC in 2006. The pricing of Alibaba's IPO on Thursday at $68 per share initially raised $21.8 billion.

Alibaba and several shareholders sold 320.1 million American Depositary Shares in the offering. But according to the IPO prospectus, underwriters had the option to sell additional shares from Alibaba, Yahoo and Alibaba co-founders Jack Ma and Joe Tsai to meet high investor demand.

The most actively traded stock on the Nasdaq, Yahoo fell nearly 6 percent on Monday to below $40 a share.

Most Chinese tech stocks listed in the United States, such as search engine Baidu and microblog site Weibo, fell an average of 4 percent on Monday.

Alibaba began trading on the New York Stock Exchange on Friday with a bang, soaring 38 percent to close at $93.89 per share.

At least 12 other firms, including Chinese ones, are expected to go public this week, for a total of $7.5 billion in new stock.

Reuters and CNBC's Bob Pisani contributed to this report.