Alibaba Group has filed for a Hong Kong IPO, most likely in the third quarter.

Documentation for the filing was lodged confidentially but has been confirmed by Reuters sources.  

As previously reported, the listing could raise as much as $US20 billion in additional capital, which is $5 billion less than its 2014 New York listing, but still a significant war chest for expansion. It may also settle for a lesser figure.

A listing in Hong Kong would give Chinese nationals an opportunity to invest in the company for the first time, due to connections between Hong Kong, Shanghai and Shenzhen.

Alibaba remains tight-lipped about its plans and has declined any comment on the listing plan.

According to Reuters and Bloomberg sources, the Hong Kong IPO will be led by investment banks China International Capital Corp and Credit Suisse Group.

Alibaba has almost doubled in size since it was listed on the New York Stock Exchange with a market value now estimated at more than $400 billion.