If approved by a simple majority of the voting power, the combination will become effective in January 2017, said Nakao.

Cooperation with AIIB

When asked about cooperation between the ADB and the AIIB during the press conference, Nakao reiterated that China's proposal of establishing the AIIB is understandable.

"The ADB will cooperate and co-finance with the AIIB on infrastructure financing across Asia by using our long experience and expertise in the region," said Nakao, noting that 80 percent of the ADB's current operations are related to infrastructure construction under the more general term of poverty reduction.

Nakao said he met with Jin Liqun, secretary general of the Multilateral Interim Secretariat of the AIIB, on the sidelines of the ADB's 48th Annual Meeting on Friday.

During the meeting, the two sides discussed for an hour on future collaboration, including co-financing, and confirmed their commitment to working together for Asia.

"We acknowledged the large infrastructure gap in the region, the critical role of infrastructure in supporting sustainable development and poverty reduction, and the importance of safeguard policies on environmental and social impacts of projects," Said Nakao.

The two sides also agreed to continue sharing necessary information and further discuss concrete options for collaboration, said Nakao.

Under the theme of Fostering Partnership for Development, the 48th ADB Annual Meeting, which opens Saturday and will last till Tuesday, has attracted about 3,000 government officials, business leaders, academics and representatives from civil society and development organizations.

Established in 1966, the ADB now is owned by 67 members, with 48 from the region. It is the first time for the annual meeting to take place in the South Caucasus region.

In 2014, the ADB's assistance totaled $22.9 billion, including co-financing of $9.2 billion.