Baltimore's Key Bridge collapses after ship collision

Rescue efforts are underway following the collapse of the Key Bridge in Baltimore, Maryland after a cargo ship collided with it. 

Multiple videos shared to social media early on Tuesday morning (local time) show a large ship running into a pillar supporting the bridge, causing it to crash down.

The videos appear to show multiple vehicles were on the bridge at the time it collapsed, with local media reporting at least 20 people are in the water.

The Baltimore City Fire Department told CBS News it was unclear how many vehicles were crossing the bridge at the time, but "there was surely a large tractor-trailer" on it.

CBS News reported multiple people are in the Patapsco River, and "the dive and rescue team has arrived on scene".

Director of communications for the Baltimore Fire Department, Kevin Cartwright, has described the incident to the Associated Press as a "developing mass casualty event".

"Our focus right now is trying to rescue and recover these people," Cartwright said.

Speaking with Good Morning Britain, he confirmed the vessel collided with a column supporting the bridge.

"We have a mass casualty, multi-agency rescue incident currently underway."

He said dive teams are currently at the scene searching for the missing individuals.

He said authorities believe there were also pedestrians on the bridge at the time it collapsed.

Cartwright told CNN that "freezing temperatures" in the water "pose concern" as rescue efforts continue.

"It feels like at least about 30 degrees [Fahrenheit] (-1C) where I am. It could be slightly lower than that," he said.

"I'm sure that the water temperature is even colder... and that can pose a concern and risk for our divers."

The bridge was struck by the Singapore-flagged Dali container ship, its owners confirmed to The New York Times. The vessel was on its way to Colombo in Sri Lanka when the disaster happened.

It's unclear at this stage what caused the ship to hit the bridge, however video appears to show it lose power and start smoking directly beforehand.

David McFarlane, director of Maritime Risk and Safety Consultants Ltd, told Sky News: "The most likely cause of this is a failure in machinery or steering gear, but we just won't know until the authorities have been on board. And even then, they're unlikely to say what's been going on for some considerable time."