A major bridge collapsed in Baltimore on Tuesday, blocking one of the busiest US commercial harbours, after a heavily laden cargo ship lost power and smashed into a support column despite desperate attempts to stop in time.
Six people - all members of a nighttime construction crew repairing potholes on the Francis Scott Key Bridge - were missing, officials said.
Maryland Governor Wes Moore told reporters that quick thinking by authorities once the ship issued a Mayday call allowed officials to stop vehicles from going onto the bridge.
"We're thankful that between the Mayday and the collapse that we had officials who were able to begin to stop the flow of traffic," Moore said. "These people are heroes. They saved lives last night."
The 1:30 am (0530 GMT) disaster occurred at dramatic speed, with video footage capturing the moment the ship, piled high with containers, slammed into one of the bridge supports, instead of passing safely under.
Almost immediately, the steel structure, which was opened in 1977, collapsed like a deck of cards.
The number of casualties was still unclear, with divers and other specialist rescue teams combing the frigid waters of the Patapsco River that lead into the bustling industrial harbour just north of the capital Washington.
In addition to the six missing construction workers, two others from the same team were rescued, with one of them severely injured.
"God willing, they can make it alive out of this," Jesus Campos, another employee at Brawner Builders Inc, of his missing colleagues.
The FBI and other agencies stressed that there was no known connection to terrorism.
"The preliminary investigation points to an accident," Moore said.
The governor, a rising star in the Democratic party, also said there was no indication that the bridge was structurally at fault, noting that it "was actually fully up to code" -- meaning it had been inspected and met safety requirements.
"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," Paul Wiedefeld, the Maryland transportation chief, said.
President Joe Biden called the collapse a "terrible accident," and pledged to get the port back up and running as soon as possible.
He also said the bridge would be rebuilt, but admitted it would "take some time."
Attempt to drop anchors
As the sun rose over Baltimore, twisted steel girders could be seen draped over the deck of the ship that was jammed under the debris of the bridge.
Details emerged on how the crew tried to avert disaster after their ship lost power and began careening toward the bridge.
"Just prior to the incident, the vessel, Dali, had experienced momentary loss of propulsion. As a result, it was unable to maintain the desired heading and collided," said the maritime authority for Singapore, where the Dali is flagged.
This authority said the ship's management company, Synergy Marine Pte Ltd, reported the crew "dropped anchors" in a last-ditch attempt to hold the ship back.
The Francis Scott Key Bridge, named after the poet who penned the lyrics to the US national anthem, is an important link in the US east coast highway system, used by about 34,000 vehicles every day.
There are other bridges and tunnels for drivers to cross the harbor. However, the tangled steel barrier now lying half-submerged across the harbor entrance blocks almost all maritime traffic.
The Port of Baltimore is the ninth-busiest major US port in terms of both foreign cargo handled and foreign cargo value, and is directly responsible for more than 15,000 jobs, supporting almost 140,000 more.
"The words that 'the Key Bridge is gone,' it still shakes us, because for over 47 years, that's all we've known... It's heartbreaking," Moore said.
Baltimore Mayor Brandon Scott described the bridge as an "unthinkable tragedy... like something out of an action movie."
"We have to be thinking about the families and people impacted," he said.
Donald Heinbuch, a former Baltimore firefighter, said he could see the bridge from his bedroom window.
"We were awakened by what appeared to be an earthquake and a long, rolling sound of thunder," he told local media.
Agence France-Presse