BEIJING, September 27 (Xinhua) -- China's largest commercial bank, the Industrial and Commercial Bank of China (ICBC), issued its prospectus Wednesday, ushering in the largest ever initial public offering (IPO) on China's stock market.

ICBC is expected to issue 13 billion A shares that will list on the Shanghai Stock Exchange.

If the over-allotment option is exercised, the total number of shares will rise to 14.95 billion, the prospectus says.

ICBC's IPO was formally approved by the China Securities Regulatory Commission (CSRC) on Tuesday.

ICBC has already started the road show for up to 40.7 billion H shares that will be listed on the Hong Kong stock exchange.

Trading of ICBC shares is expected to start on the Shanghai and Hong Kong bourses on October 27.

ICBC will be the first major Chinese firm to list on the mainland and overseas stock markets at the same time. Many blue chips from China list first on overseas markets before registering on domestic exchanges, drawing increasing criticism from mainland investors.

Going public is part of the Chinese government's plan to overhaul its banking system and prod state-owned banks into improving their corporate governance.

ICBC is the third of the "Big Four" state-owned commercial banks to list on the stock market after the Bank of China and China Construction Bank.

The fourth one, the Agricultural Bank of China, is also being restructured for a possible IPO.

As the largest commercial bank in China, ICBC has 2.5 million corporate customers and some 150 million individual customers.

By the end of 2005, the bank held assets worth 6.46 trillion yuan (816 billion U.S. dollars), a deposit balance of 5.74 trillion yuan and a lending balance of 3.29 trillion yuan.

The bank recorded a pre-tax profit of 38.6 billion yuan in the first half of 2006, up 9.1 percent year on year, the prospectus says.