The steel arch Francis Scott Key Bridge in Baltimore, Maryland collapsed into the Patapsco River early Tuesday morning after a main pillar was struck by a cargo ship.
"Key Bridge collapse due to ship strike. Active scene," the Maryland Transportation Authority said in a post on X, formerly Twitter. Transport authorities added that traffic was being detoured from the I-695 highway, a key link in the city that crosses the bridge.
The 1.6-mile (2.57 kilometer) bridge, which was completed in 1977, spans a wide section of the Patapsco River in southern Baltimore on the US east coast.
Videos shared on social media showed multiple vehicles falling into the river after the collision. The incident took place at 1:35 a.m. local time, according to Baltimore police.
The mayor of Baltimore said emergency personnel were on scene and rescue efforts were underway.
"Emergency personnel are on scene, and efforts are underway," Baltimore Mayor Brandon M. Scott wrote on X.
Kevin Cartwright, the director of communications for the Baltimore Fire Department, told the Baltimore Sun newspaper that the "entire bridge collapsed into the Patapsco River."
"We have reason to believe that there were vehicles and possibly a tractor-trailer" that fell into the water, he said, adding that the number of vehicles is unknown.
Rescue efforts ongoing
Later Tuesday morning, Maryland Governor Wes Moore declared a state of emergency.
"We are working with an interagency team to quickly deploy federal resources from the Biden Administration," Moore posted on X.
Cartwright told The Associated Press news agency that multiple vehicles were on the bridge at the time the vessel struck one of its columns.
He described the collapse as a "developing mass casualty event."
"This is a dire emergency," he said.
What caused the collision?
After the incident, the Synergy Marine Group confirmed that its Singapore-flagged vessel Dali with two pilots onboard collided with one of the bridge's pillars, according to Reuters news agency.
There were no injuries onboard, a Synergy statement said.
"The exact cause of the incident is yet to be determined," it added.
Danish shipping company Maersk later announced that it chartered the Dali vessel.
"We are horrified by what has happened in Baltimore, and our thoughts are with all of those affected," Maersk said in a statement.