A portion of a bridge in the US state of Maryland has collapsed after a large boat struck it, causing multiple vehicles to fall into the water under.

At about 1.30am (local time), a large vessel crashed into Baltimore’s Francis Scott Key Bridge, catching on fire before sinking, according to a video posted on X, formerly known as Twitter.

The director of communications for the Baltimore Fire Department, Kevin Cartwright told Associated Press that emergency responders were searching for at least seven people believed to be in the water at about 3 am (local time).

He said agencies received 911 calls at about 1.30am (local time) reporting a vessel traveling outbound from Baltimore that had struck a column on the bridge, causing it to collapse.

Multiple vehicles were on the bridge at the time, including one the size of a tractor-trailer.

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

He said it was too early to know how many people were affected but called the collapse a “developing mass casualty event.”

Cartwright said it appeared there are “some cargo or retainers hanging from the bridge,” creating unsafe and unstable conditions, and that emergency responders are operating cautiously as a result.

“This is a dire emergency,” he said.

The Maryland Transportation Authority said all lanes closed both directions for incident on I-695 Key Bridge and traffic is being detoured.

Mayor Brandon M. Scott and Baltimore County Executive Johnny Olszewski Jr. said emergency personnel were on the scene and rescue efforts were underway.

The Francis Scott Key Bridge opened in 1977.

The four-lane bridge extends over the Patapsco River and serves as the outermost crossing of Baltimore’s harbour and an essential link of Interstate-695, or the Baltimore Beltway.

More to come….