BEIJING, Jan 29 (Reuters) - Bank of China Ltd. said it plans to sell up to 150 billion yuan ($21 billion) of loss-absorbing bonds, becoming the nation's first big state bank to plug a major funding shortfall before a 2025 deadline to meet global capital requirements.

The lender said it plans to tap both domestic and overseas debt markets to sell a new category of total loss-absorbing capacity (TLAC) bonds, according to a Friday filing with the Shanghai Stock Exchange.

China's banking regulator in 2022 allowed the nation's major state-owned banks to issue the TLAC bonds, in a move it said would help prevent any potential instability in its financial system.

The loss-absorbing bonds, which are not counted in a bank's capital base, can be written off, or converted into common equities, when the bank enters the disposal phase.

China's top five lenders - Industrial and Commercial Bank of China, Agricultural Bank of China Ltd, Bank of China, China Construction Bank and Bank of Communications - are designated as global systemically important banks by Chinese regulators and the Switzerland-based Financial Stability Board (FSB).

The global systemically important lenders are required to hold a TLAC amount of at least 16% of risk-weighted assets starting Jan. 1, 2025, and the bar will be further raised to 18% from Jan. 1, 2028.

The requirements will add to the Chinese lenders' capital-raising pressure, said Fitch Ratings in a recent note, especially if the banks are under greater strain to support the Chinese economy, property developers and local government financing vehicles.

To meet the requirements, other lenders are also expected to unveil loss-absorbing bond issuance plans soon. The five banks are estimated to issue additional 1.7 trillion yuan debt by 2025 and 6.3 trillion yuan by 2028 to plug capital shortfalls to meet the TLAC requirements, Fitch estimated.

($1 = 7.1827 yuan) (Reporting by Ziyi Tang and Ryan Woo Editing by Shri Navaratnam)