China-led Asian Infrastructure Investment Bank is officially open for business after a formal ceremony led by Chinese President Xi Jinping.

Representatives from 57 member countries attended the event Saturday, when China announced it would pledge $50 million to a special fund to prepare less developed countries for infrastructure projects.

The United States and Japan are not members of AIIB, saying it is a rival to already existing multilateral banks such as the World Bank, but Beijing says the AIIB supplements existing institutions and will boost investments for infrastructure projects in Asia.

The bank also is a key part of Beijing's "One Belt One Road" outreach to extend China's economic influence in the region.

Beijing has pledged to put up most of the bank's initial $50 billion in capital.