US President Donald Trump has approved a major disaster declaration for the Commonwealth of the Northern Mariana Islands (CNMI), unlocking federal disaster assistance for residents of Rota nearly a month after Super Typhoon Bavi devastated the island.

The declaration makes eligible households on Rota able to apply for the Federal Emergency Management Agency (FEMA) Individual Assistance and expands federal support for government recovery efforts.

The declaration covers damage from Bavi between 4-12 July.

The Category 5 storm damaged more than half of Rota's buildings, knocked out power and water across the island, and severely damaged critical infrastructure.

Federal Public Assistance will also cover all eligible recovery work on Rota and emergency protective measures on Saipan and Tinian, with direct federal assistance on Rota funded at 100 percent of eligible costs for the next 90 days.

Rota senator Paul Manglona welcomed the announcement.

"On behalf of the people of the CNMI and the island of Rota in particular, I want to express our sincere gratitude to President Donald J. Trump for issuing a Major Disaster Declaration," Manglona said.

"This action will make federal assistance available to help our people and communities recover and rebuild in the wake of Super Typhoon Bavi."

Rota representative Julie Marie Ogo said the declaration would provide "critical federal assistance" to help families, businesses and communities recover. She also noted that many residents continue to face hardship and that the island remains without grid power. Her office is assisting residents with FEMA disaster assistance applications.

Rota Chamber of Commerce acting president Juan Pan Guerrero said the assistance was overdue.

"It's about time that Fema relief arrive 1 month after ST Bavi," Guerrero said.

He said restoring electricity would reduce costs for residents who have relied on generators since the storm.