The US National Flood Insurance Program (NFIP) continues to face a massive deficit bill adding to growing concerns over its future management.

A Government Accountability Office (GAO) report has revealed the scheme is unlikely to generate sufficient revenue to repay the $US18.5 billon ($18.2 billion) borrowed from the US Treasury to cover claims from the 2005 hurricane season and any future catastrophe losses.

The GAO believes this highlights structural weaknesses in how the program is funded and run by the Federal Emergency Management Agency (FEMA).

“While FEMA has taken some steps to address these issues, including increasing the number of policyholders and implementing new contractor oversight processes, it continues to face complex challenges,” the report says.

“Congress needs to act to restructure the program.”

The GAO says weaknesses in the management and operations of the NFIP also create a risk that the funds allocated to the program and the premiums paid by policyholders are not being used efficiently or effectively.

A detailed report will be submitted to the Government in March.