US insurers have joined other business groups in pushing Congress to extend the National Flood Insurance Program (NFIP), which was due to expire last Friday.

Failure to renew the program will leave millions of Americans at risk and may delay recovery efforts related to recent hurricanes Florence and Michael.

“Flooding is the most common and costly natural disaster in the US,” the insurers say in a joint letter to congressional leaders.

“The NFIP is the main source of flood insurance in the US, and Americans deserve certainty and stability in the flood insurance marketplace to protect their homes and loved ones.”

Signatories include the Risk and Insurance Management Society (RIMS), the Property and Casualty Insurers Association of America, the American Insurance Association and the Reinsurance Association of America.

“A lapse in NFIP coverage would be devastating for thousands of businesses across the US,” RIMS CEO Mary Roth said.

“For too long, the program has received temporary extensions.”

The federal program has required several stopgap extensions as Congress struggles to hammer out a long-term reauthorisation plan.

The scheme is losing about $US1.4 billion ($1.9 billion) every year and now owes the US Treasury more than $US20 billion ($27.3 billion).