Industrial and Commercial Bank of China (ICBC) is raising the number of shares in its stock flotation by 15%, citing overwhelming demand from investors.
ICBC's shares have proved to be very popular
Shares in the bank, China's biggest lender, are due to float on Friday in a dual-listing on the Shanghai and Hong Kong stock exchanges.
ICBC said it would now issue an extra 1.95 billion shares in Shanghai.
If the bank, as expected, also adds more shares in Hong Kong, the value of the float could rise to $22bn (£12bn).
Prior to the announcement of extra shares in Shanghai, it was already on target to make $19bn, itself a new global record high for a share flotation.
ICBC said the float was 50 times over-subscribed.
OTHER RECENT BANK FLOATS
China Merchants - $2.4bn
Bank of China - $11.2bn
China Construction - $8bn
The previous record for the world's largest initial share flotation was $18.4bn, which was raised by Japan's NTT Mobile Communications Network in 1998.
China's surging economy has created huge demand for banking services and forced the sector to modernise.
Share offerings are part of this process - prior to ICBC, four lenders had raised $25bn by listing since June 2005.
Industrial and Commercial Bank of China was set up by the Chinese government in 1984 and has 21,000 branches, 360,000 staff and 150 million customers.