Baltimore’s Key Bridge collapsed after it was hit by a container ship, sending cars that were crossing at the time plunging into the waters of the Patapsco River.

At least seven people are believed to be in the water and rescue efforts are ongoing at the site of the collapse, according to the Baltimore Fire Department.

Multiple videos shared on social media showed a large cargo ship ramming into one of the bridge’s support pillars, causing it to come crashing down into the river.

Bridge in Baltimore, Maryland fell. Pray for everyone involved 🙏🏾 pic.twitter.com/E4GA7CWOfM
— FearBuck (@FearedBuck) March 26, 2024

A large portion of the Francis Scott Key Bridge is now under water, as flight tracking website FlightRadar24 showed the Maryland State Police circling the site of the crash in a helicopter.

Kevin Cartwright, director of communications for the fire department, said the city was dealing with a “developing mass casualty incident”.

The 911 calls relating to the incident began from around 1.30am, he said, as members of the public said a vessel travelling out of Baltimore’s port had struck a column on the bridge. Multiple vehicles, including one the size of a tractor-trailer, were on the bridge at the time of strike.

"Our focus right now is trying to rescue and recover these people," Mr Cartwright said, adding that its too early to know how many people are affected.

There are “some cargo or retainers hanging from the bridge”, he said, creating unsafe and unstable conditions. Emergency responders are operating cautiously. "This is a dire emergency," he added.

The 47-year-old Key Bridge collapsed due to a “ship strike” incident and has been closed to traffic, the Maryland Transportation Authority said on X in a statement.

“All lanes closed both directions for incident on I-695 Key Bridge. Traffic is being detoured,” it said.

Whom to blame?

Sky News reported that a maritime safety expert says the "most likely" cause of the crash was a failure in the ship's machinery.

David McFarlane, director of Maritime Risk and Safety Consultants Ltd, told Sky News: "The first thing that springs to my mind is: was there a sudden fault with the ship's engines or the steering gear? The other, of course, is: was there a navigational error?"

Mr McFarlane said a human error was less likely because of the number of people who would have been on duty.

"There should be no room for one person errors because one of the other people should jump in and say 'hang on...'," he said.

"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."

Water temperature below 10C

The US's National Oceanic and Atmospheric Administration says the current water temperature in Baltimore Harbour is between 9-10C.

The New York Times cites the US's national public health agency as saying hypothermia can occur in any water temperature below 21C.

The NHS describes hypothermia as a dangerous drop-in.