WASHINGTON − As many as 600 people are still missing in the wake of Hurricane Helene, President Joe Biden said Monday, promising devastated communities that help is on the way and the "nation has your back" in a speech Monday at the White House.

"We'll continue to serve resources including food, water, communications, and lifesaving equipment will be there," Biden said. "I mean it − as long as it takes to finish this job."

He also said he's committed to travel later this week to affected communities.

"I've been told that it would be disruptive if I did it right now," he said.

Authorities are dealing with the storm's aftermath, which saw caused widespread devastation and power outages across the Southeast and killed at least 100. Biden, who said he's been in touch with governors, mayors and local leaders, said 600 people were still unaccounted for.

That number fell from 1,000 overnight after cellular phone service was restored to some areas.

The president said he'd directed his team to provide "every available resource, as fast as possible, to your communities, to rescue, recover, and to begin rebuilding."

In addition to FEMA, the effort includes the Federal Communications Commission to help establish communications capability. The National Guard, the Army Corps of Engineers and the Department of Defense will all be providing resources to rescue and assist in clearing debris and delivering life saving supplies, he said.

Millions of people across multiple states are dealing with power outages, destroyed roads and bridges and flattened buildings. The damage was experienced across Florida, Georgia, North Carolina, South Carolina, Alabama, Tennessee and Virginia.

More:How can I help those affected by Hurricane Helene? Here are ways you can donate

The record-breaking storm hit Florida as a hurricane on Thursday with wind speeds of 140 mph has since weakened to a post-tropical cyclone with 25 mph winds.

On Sunday, Biden approved major disaster declarations for the states of Florida and North Carolina, allowing survivors to immediately access funds and begin recovery efforts. People in 17 counties in Florida and 25 counties in North Carolina, including the Eastern Band of Cherokee Indians, can now apply for assistance with FEMA, according to a fact sheet provided by the White House.

FEMA Administrator Deanne Criswell visited Florida over the weekend to assess damage alongside local and state officials. She continued surveying damage Sunday in parts of Georgia and will be leaving for North Carolina on Monday, according to the White House.

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More than 3,300 personnel from across the federal workforce are deployed and supporting Hurricane Helene response efforts across the states, according to the White House.

Vice President Kamala Harris planned to cut short a campaign trip in Nevada on Monday and will visit the FEMA headquarters to hear about the federal actions being taken to support emergency response and recovery, a White House official said.

This story was updated to add a video.

Contributing: Reuters

Swapna Venugopal Ramaswamy is a White House Correspondent for USA TODAY. You can follow her on X @SwapnaVenugopal