Japan will fall from being the second-largest contributor to the United Nations' general budget to third place starting next year as China gets set to surpass it, according to diplomats.

China's contribution will rise to 12.01 percent while Japan's will fall to 8.56 percent for the 2019 to 2021 period, according to the new scale agreed on by U.N. members, which will formally adopted by the General Assembly, possibly Saturday.

"According to the new scale of assessments initially agreed upon, starting from 2019, China will become the second-largest financial contributor to the U.N.'s regular budget," a Chinese delegate said after the committee decision. "For a developing country with about a 1.4 billion population, this is not a small amount."