Industrial & Commercial Bank of China Ltd (ICBC), the world's biggest commercial bank by market value, kicked off a two-day sale of subordinated bonds valued at 50 billion yuan ($7.9 billion) to replenish its capital on Thursday.

The sale consists of 10-year bonds valued at 10 billion yuan and 15-year securities of 40 billion yuan, according to a statement posted on Chinabond.com, the nation's major debt clearing house.

ICBC sold subordinated bonds worth 38 billion yuan in June. Adding in the 50 billion yuan, the lender has raised a total of 88 billion yuan in bond sales this year.

In November, ICBC shareholders approved plans to raise as much as 70 billion yuan through bond sales by the end of June 2012, which means it will probably sell bonds totaling 20 billion yuan before that date.

Yang Kaisheng, ICBC's president, said in November that the bank doesn't have any other equity-financing plan.

At the end of September, ICBC registered a capital-adequacy ratio (CAR) of 12.51 percent and a core CAR of 10.03 percent.

The government's new tougher level for major lenders' CAR is 11.5 percent. The requirement for core CAR stands at 9.5 percent. The regulations are scheduled to take effect at the beginning of 2012.

Facing higher capital requirements, increased lending due to relatively looser credit controls next year, and declining deposits, banks have been seeking to raise more capital through all available channels.

The high threshold of equity-financing approval in a bearish stock market has increased lenders' interest in raising money through selling bonds.

Shares of China's five biggest banks - which raised a combined $61.5 billion from equities last year - have lost an average 22 percent this year on concern that a record two-year credit boom may unravel and lead to rising bad debts, according to Bloomberg.

In 2011, commercial lenders in China have raised more than 300 billion yuan to bolster their capital by selling subordinated bonds, an increase of 2.4 times on last year's 90 billion yuan.

Meanwhile, the five biggest banks sold bonds worth 236 billion yuan this year, accounting for 75 percent of total bond issuance.

"The increasing issuance of debt in the interbank market will gradually lead to a deterioration of the asset quality of commercial lenders," said Guo Tianyong, director of the Research Center of the Chinese Banking Industry at the Central University of Finance and Economics.

Rather than postponing implementation of the new requirements, Guo suggested that the China Banking Regulatory Commission (CBRC) should allow lenders to add medium- and long-term deposits, such as five-year deposits, into the capital category to obtain a higher CAR.

Officials at the CBRC have urged commercial lenders to rely on themselves when they seek more capital, instead of eyeing external sources.