Fiji's government faces the challenge of raising billions of dollars for strengthening its resilience against climate change if it is to avoid pushing public debts into unsustainable levels, a new report has found.

The World Bank Group examined how Fiji can strengthen its ability to adapt to climate change while continuing to develop its economy.

Its Country Climate and Development Report assessed climate risks, resilience measures and investment priorities and found the Pacific island state needs additional climate financing from between 4.8 and 7.8 percent of its gross domestic product annually from 2026 until 2050 to counter the threat.

The report said traditional borrowing alone will not meet the needs of the challenge to finance critical infrastructure and adaptation projects, which will require a combination of international assistance, domestic fiscal reforms and private-sector investment.

"This amounts to $US411 million to US$647 million ($A588.3million to $A926.1million) in each of the five years from 2026 to 2030 and $US326 million to $US547 million ($A466.5 million to $A782.9 million) in each of the 20 years from 2031 to 2050," the report said.

It found Fiji's financing needs will be higher in the near term, driven largely by costly upgrades to existing infrastructure and efforts to reduce emissions in its energy and transport sectors.

The report estimated that potential additional financing sources at an average of 3.1 percent of Fiji's GDP annually, equivalent to about $US249 million ($A356.4 million) will be required between the 24-year period under both "investment scenarios".

Much of this funding is expected to come from international public finance and potential revenue from higher duties on imported fuel.

"Carbon finance is likely to be relatively limited," the report stated, "however, there is also an opportunity to further utilise green and blue bonds".

The report noted Fiji's government has limited fiscal space, highlighting the urgent need to increase its revenue or consolidate spending to support climate investment.

Green and blue bonds - financial instruments used to raise money for a required environmental project - may help attract new investors to climate-related projects, while concessional loans and donor grants would provide alternative funding sources.

The report also recommended domestic reforms including broadening its revenue base, phasing out inefficient fossil fuel subsidies, and strengthening public financial management.

Adaptation can also offset much of the financial damage, raising the GDP by 3 to 5.7 per cent by 2050, which is also estimated to create 5,300 additional jobs in the next four years alone.

Debt-for-climate swaps and risk-sharing facilities could further ease repayment pressures and free up resources for resilience projects, the report added.

The country's own financial sector was suggested of being capable of helping bridge funding shortfalls.

"Fiji's financial sector is deep relative to SIDS' (Small Island Developing States) peers and could help to close the climate financial gap," the report found.