President Joe Biden gave remarks Tuesday on the Baltimore bridge collapse, telling residents "we're going to stay with you as long as it takes."

"It's my intention that the federal government will pay for the entire cost of reconstruction in that bridge. I expect the Congress to support my effort," Biden said from the White House.

"This is going to take some time," the president said, adding, "We're not leaving until this job gets done."

Personnel on the ship alerted the Maryland Department of Transportation that they lost control of the vessel, and local authorities were able to close the bridge before it was struck, "which undoubtedly saved lives," Biden told reporters.

A cargo ship crashed into Baltimore's Francis Scott Key Bridge early Tuesday morning, causing a near-total collapse of the span and halting vessel traffic into and out of the Port of Baltimore.

A search-and-rescue effort is underway, with divers and emergency personnel desperately combing the Patapsco River for people believed to have fallen from the collapsing bridge into the frigid water below, officials said. At least six people are unaccounted for, officials said.

It appears the crash was a "terrible accident," Biden said.

He said the search and rescue operation is the top priority.

Biden, who noted he's been over the bridge many times, said he plans to visit Baltimore as soon as possible.

"Ship traffic and the port of Baltimore has been suspended until further notice. And we'll need to clear that channel before the ship traffic can resume," the president said.

"Our prayers are with everyone involved in this terrible accident and all the families, especially those waiting for news of their loved one right now," Biden said. "I know every minute in that circumstance feels like a lifetime, you just don't know. It's just terrible."

"We're incredibly grateful for the brave rescuers who immediately rushed to the scene and to the people of Baltimore. I want to say, we're with you," the president said. "We're going to stay with you, as long as it takes. And like the governor said, 'you're Maryland tough, you're Baltimore strong and we're going to get through this together.'"

Biden convened senior members of his team Tuesday morning for a briefing on the ongoing response and directed them to ensure all federal resources are made available, the White House said.

ABC News' Mariam Khan, Kevin Shalvey and Emily Shapiro contributed to this report.