The China-backed Asian Infrastructure Investment Bank (AIIB), viewed by some as a rival to the World Bank and Asian Development Bank, was formally established on Friday, according to a statement issued by Beijing.

The United States and Japan -- the world's largest and third-largest economies, respectively -- have notably declined to join the bank, which is expected to begin operations early next year, though others such as Australia, Germany and Britain will take part.

It will be operational once its board of directors and executive council have met for the first time at an opening ceremony scheduled for January 16-18, the ministry of finance said in a statement on its official website.

Beijing will be by far the largest AIIB shareholder at about 30 percent, according to the legal framework signed by 50 founding member countries in late June.

The bank is headquartered in Beijing and currently has 57 members.

With authorised capital of $100 billion, it expects to offer its first batch of project loans by mid-2016, according to the official Xinhua news agency.