President Biden told the people of Baltimore on Friday that “your nation has your back” as he stood in front of the collapsed Francis Scott Key Bridge, which was destroyed after a cargo ship plowed through it last week, killing six people.

Mr. Biden encountered a tangle more than a mile long of concrete and steel that has snarled traffic, devastated blue-collar communities and disrupted operations at one of America’s biggest ports, threatening chaos that could ripple across supply chains.

“We’re going to move heaven and earth to rebuild this bridge as rapidly as humanly possible,” Mr. Biden said. He called on Congress to help fulfill his promise that the federal government to pay to rebuild the bridge.

Mr. Biden took an aerial tour of the damage and received a briefing from officials overseeing the cleanup and rebuilding efforts, before meeting privately with families of six construction workers who plunged into the Patapsco River when the bridge collapsed.

“The damage is devastating, and our hearts are still breaking,” he said in his public remarks.

Mr. Biden described how the workers had been on a break from filling potholes right before disaster struck. Just seconds before, Mr. Biden said, one of the men, a 24-year-old, sent a message to his girlfriend that said, “We just poured cement, and we’re waiting for it to dry.”

“We’ll also never forget the contributions these men made to this city,” Mr. Biden said. “We’re going to keep working hard to recover each of them.”

In the week since the collapse, the administration has funded the harbor cleanup, unlocked $60 million in emergency funding to help rebuild the bridge, provided low-interest disaster loans to affected businesses and overseen efforts to manage any supply chain disruptions.

On Friday, Mr. Biden called on companies to commit to keeping employees — about 20,000 people depend on the port for jobs — on their payrolls as the port reopens. This week, senior administration officials, including Mr. Biden’s chief of staff, called major employers in the Baltimore area, including retail chains such as Home Depot and distributors like Amazon, to encourage them to retain workers.

Local and federal officials said the road to recovery would be long.

“As you can see behind me the physical impact of this tragedy is massive,” said Baltimore Mayor Brandon Scott. “But let’s be clear, the human impact is immeasurable.”

At a briefing on response efforts, Brig. Gen. John P. Lloyd from the U.S. Army Corps of Engineers described a “mangled mess” that was being tackled by 51 divers and 12 cranes. He told the president that one pending task was to remove a large section of the bridge sitting on the ship. The section weighs 5,000 tons and is 125 feet high.

The bridge crumbled in the dead of night when a 985-foot-long cargo vessel crashed into it shortly after departing the Port of Baltimore, a vital economic engine that handles more cars and farm equipment than any other port in the country. The vessel, the Dali, lost power before it hit the bridge but sent a mayday call that gave officials enough time to halt bridge traffic.

But it was not enough time to get to workers who were already on the bridge.

The bodies of two of the workers were recovered from the river on March 27. Recovery efforts for the remaining workers, who are presumed dead, were suspended. The authorities said the bodies were most likely encased in steel and concrete.

Mr. Biden spoke affectionately of his own ties to the port of Baltimore, including his family who worked as watermen in the 1850s and his many years commuting from Delaware.

The structure, which took five years to build, opened in 1977 and served as a critical transportation link on the East Coast. It was named after Francis Scott Key, the Maryland-born author of “The Star-Spangled Banner.”

Mr. Biden’s response drew praise from Gov. Wes Moore, who said he received the first call from the White House at around 3 a.m., just 90 minutes after the collision.

“And every hour since we’ve worked hand in hand with this administration,” Mr. Moore said. “President Biden might not be a Marylander by birth. But I tell you, he’s proven what it means to be Maryland tough, and Baltimore strong.”

Scott Cowan, the president of the local chapter of the International Longshoremen’s Association, said he was encouraged by Mr. Biden’s visit but believed there was more to be done.

As the weeks go by, Mr. Cowan said, the situation for the 2,400 members of his local was getting more difficult. Around 400 people in the local were working at the moment, he said, with around 2,000 idled, roughly the inverse of the normal ratio.

If it had been a gradual work slowdown, people could have adjusted, he said, but “it was like hitting a wall” when the bridge collapsed and all but shut down the port.

“President Biden does know about ports,” Mr. Cowan said. “I think he wants to do so something. But obviously there’s Congress involved too.”

Campbell Robertson contributed reporting from Baltimore.