A cargo ship hit a major bridge in the eastern US city of Baltimore, Maryland, in the early hours of Tuesday, causing it to collapse and plunging several people into the frigid river below.
The six people, who were carrying out maintenance work on the bridge at the time, are presumed dead.
"At this point we do not believe that we're going to find any of these individuals still alive," Coast Guard Rear Admiral Shannon Gilreath said.
Officials suspended search and rescue operations on Tuesday evening.
Two people were rescued from the water earlier, Baltimore City Fire Department Chief James Wallace told reporters.
One of the people pulled from the river refused medical treatment, while another was seriously injured and is being treated at a trauma centre, Mr Wallace said.
Baltimore Mayor Brandon Scott described the scene as unbelievable and like “something out of an action movie”, after footage showed a large section of the 2.6km Francis Scott Key Bridge toppling into the Patapsco River at about 1.30am.
The ship involved in the incident, the Singapore-flagged container vessel Dali, appeared to lose power before it struck the bridge, and footage showing large plumes of smoke rising from the ship was shared online.
Officials have declared a citywide state of emergency.
The river is as deep as 15 metres in some areas, Baltimore's fire department confirmed.
Wind, frigid temperatures and murky waters made rescue teams' working conditions difficult.
“We're going to send all the federal resources they need as we respond to this emergency, I mean all the federal resources and we're going to rebuild that port together,” President Joe Biden said from the White House.
“Everything so far indicates that this was a terrible accident. At this time, we have no other indication, no other reason to believe and if any intentional acts here.”
Witnesses heard loud boom before ship struck - video
He said that the federal government would pay to repair the bridge so it can be reopened as quickly as possible.
Transportation Secretary Pete Buttigieg, on a last-minute visit to Baltimore for the incident, said it was too soon to estimate how long it would take to clear the channel and rebuild the bridge.
Mr Biden said he planned to visit the city soon.
A large lorry was crossing the bridge when it collapsed, fire department officials told CBS News, and there was reportedly a large amount of diesel in the water.
Maryland Governor Wes Moore said the bridge was “up to code” when asked if there had been any structural issues.
“We are still investigating what happened but we are quickly gathering details,” he told reporters.
“The preliminary investigation points to an accident. We haven't seen any credible evidence of a terrorist attack.”
Maryland Transport Secretary Paul Wiedefeld said the workers on the bridge had been repairing potholes at the time of the collapse.
“The crew that was out there working was basically repairing potholes, just so you understand, that had nothing to do with a structural issue at all on the facility,” Mr Wiedefeld said.
The Dali had set off from Baltimore, bound for Sri Lanka, at 1am on Tuesday.
Francis Scott Key Bridge collapse – in pictures
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A satellite image of the Dali container ship and sections of the collapsed Francis Scott Key Bridge in Baltimore, Maryland. Reuters -
People gather for a vigil at Mount Olive Baptist Church in Dundalk, Maryland. AP -
The Dali cargo ship ran into the bridge, leading to its collapse on March 26. AFP -
News crews and residents gather along the shoreline. Rescuers pulled two people from the Patapsco River but were searching for at least seven more. AFP -
Jesus Campos speaks about the work he and his co-workers normally do to repair the Francis Scott Key Bridge. AFP -
Mr Scott, centre, hugs an attendee during a vigil for victims of the bridge collapse at the Mount Olive Baptist Church in Baltimore. AFP -
Baltimore Police commissioner Richard Worley, centre, Mayor Brandon Scott, right, and Fire Department chief James Wallace hold a press conference. AFP -
Rescuers gather on the shore of the Patapsco River for an operation authorities described as a 'mass casualty, multi-agency rescue'. EPA -
Motorway alerts warn drivers about the incident in Baltimore. Reuters -
A number of workers were carrying out repairs when the Dali hit the bridge. Bloomberg -
The bridge collapsed on top of the vessel. EPA -
A large lorry was crossing the bridge when it collapsed, fire department officials said. Reuters -
The Francis Scott Key Bridge was the world's third-longest continuous truss bridge. Getty Images
Mr Moore later said an emergency call from the ship had allowed authorities to close the bridge to vehicle traffic before the collision.
The Dali's crew is safe and unhurt, the ship's management said.
“Whilst the exact cause of the incident is yet to be determined, the Dali has now mobilised its qualified individual incident response service,” said the Singapore-based Synergy Maritime Group.
Maritime traffic in and out of the port has been suspended until further notice, officials said. The area near the bridge has been declared a “no drone zone” by the Federal Aviation Administration.
The bridge carries Maryland's Interstate 695, which encircles Baltimore. It is the world's third-longest continuous truss bridge.
A critical element of the city's skyline, transit and infrastructure, the bridge was named after Baltimore poet Francis Scott Key, the author of the American national anthem, The Star-Spangled Banner.
More than a third of US bridges are in need of repair, and over 43,000 are in poor condition and classified as “structurally deficient”, the American Road and Transportation Builders Association said.
In June, a bridge collapsed in Philadelphia after a lorry carrying more than 32,000 litres of petrol crashed and caught fire on a major motorway used by about 160,000 people each day.
State authorities declared a state of emergency after the crash, which caused major disruption to traffic on the east coast and required a month of repairs.
Thirteen people were killed in a 2007 bridge collapse in Minnesota.
Investigators said the accident was caused by construction errors.
Jihan Abdalla contributed to this report from Washington
