China is expected to surpass Japan as the second-largest contributor to the general United Nations budget starting in 2019, according to the latest U.N. report on contributions.

According to a U.N. General Assembly report of the committee on contributions, China is expected to overtake Japan with its estimated contribution rising to 12.01 percent while Japan's falls to 8.56 percent for the 2019-2021 period.

The shift in power could fuel fears that Tokyo's aspiration to become a new permanent member of a revamped U.N. Security Council may fall out of reach.

For the 2016-2018 period, the scale of assessments adopted for China was 7.921 percent, while Japan is paying almost 2 percentage points more at 9.680 percent.

The scale of assessments is determined by a number of factors, including the "most current, comprehensive and comparable data" available for gross national income.

However, other variables such as conversion rates and debt-burden adjustments are also factored into the determination of how much each country will pay into the budget for the world body.

Debates to restructure the Security Council have gone on for decades with little apparent progress despite Japan's push for itself along with Germany, Brazil and India to become permanent seat holders.

The Group of Four is at loggerheads with another bloc called Uniting for Consensus, which includes such states as Pakistan, Italy, South Korea and Argentina.

Meanwhile, the African Group has been pressing to add African nations as new permanent and nonpermanent seat holders, arguing that they have long been underrepresented.

The latest projections for the general budget followed a similar change in rankings for peacekeeping operations funding. Beginning in 2016, Japan slipped to third place behind China and the United States, the top contributor.