The Key Bridge crumples after being struck by a ship, which is visible in the left of the frame. Photo: Screenshot / StreamTime Live
Warning: This story contains a video that may shock some viewers
The 3km-long Key Bridge in Baltimore, Maryland has collapsed into the water after a cargo ship collided with it.
Cars and a large tractor-trailer were on the bridge before it collapsed and a Baltimore City Fire Department spokesperson has confirmed that the collapse is a "mass casualty event".
Videos posted online showed the bridge crumpling and falling into the water at about 1.30am local time.
The Baltimore City Fire Department said up to 20 people and several vehicles fell into the river. Sonar quickly detetcted a number of vehicles in the water.
The temperature in Baltimore Harbour was about 9C at the time of the incident, according to the US National Data Buoy Centre.
At a media coneference held several hours after the collapse, Baltimore Police Chief James Wallace said two people were rescued from the water.
"One individual refused service and refused transport - essentially that person was not injured," he said.
"However, there was another individual that's been transported to a local trauma centre that is in a very serious condition."
He said the search will continue for some time.
"We are still very much in an active search and rescue posture at this point and we will continue to be for some time.
"We have a large area that we have to search. This includes on the surface of the water, subsurface, as well as on the deck of the ship itself."
The Governor of Maryland Wes Moore has declared a state of emergency, saying: "We are working with an interagency team to quickly deploy federal resources from the Biden Administration."
He thanked the "brave men and women who are carrying out efforts to rescue those involved and pray for everyone's safety".
Baltimore's mayor Brandon Scott said the event was an "unthinkable tragedy".
He said he was thinking of the families affected and thanked first responders.
"We have to be thinking about the families and people impacted, folks who we have to try to find. This is what our focus should be on right now, we're going to continue to work in partnership with every part of government to do everything we can to get us through the other side of this tragedy."
An outbound cargo ship passes under the Francis Scott Key Bridge in 2018. Photo: Mark Wilson / Getty Images / AFP
Traffic was being diverted along the interstate or through the harbour tunnel.
On marine radars, the Dali departed from the terminal at Port Breeze at around 12:45am ET (4:45am GMT). It travelled towards the Francis Scott Key Bridge, but became stationary at the site of the bridge 45 minutes later.
The bridge that collapsed is named the Francis Scott Key Bridge, or the Key Bridge for short. It is part of the 695 highway that circles Baltimore.
The shipping company Synergy Marine Group confirmed that its ship Dali collided with a pillar of the Francis Scott Key Bridge in Baltimore.
"Whilst the exact cause of the incident is yet to be determined, the 'Dali' has now mobilised its Qualified Individual Incident response service," it said.
It said all crew members were accounted for and there were no reports of injuries.
- BBC / Reuters