Fitch Ratings upgraded the viability ratings of China Construction Bank Corp., Industrial & Commercial Bank of China Ltd. and Bank of China Ltd. to "bb+" from "bb," given the banks' consistently high capital levels and loss-absorption buffers.

At the same time, the rating agency affirmed the long- and short-term issuer default ratings of the three banks, as well as Agricultural Bank of China Ltd. and Bank of Communications Co. Ltd., at A and F1, respectively. The viability ratings of Agricultural Bank of China and Bank of Communications were affirmed at "bb" and "bb-," respectively, Fitch said May 16.

The outlooks on all the five lenders are stable.

The upgrade for Bank of China's viability rating also reflects the stability of its profile in a challenging environment, its geographic diversification and adequate asset quality, Fitch said. The long-term issuer default ratings of the five banks reflect an extremely high level of support from the Chinese government in times of need, according to the rating agency.

Fitch expects Bank of Communications to become a global systemically important bank over the next one to two years unless it slows its expansion significantly. The other four banks — ICBC, Agricultural Bank of China, China Construction Bank and Bank of China — are already designated as G-SIBs.