A major bridge in Baltimore snapped and collapsed after a container ship rammed into it on Tuesday, and several vehicles fell into the river below.

Rescuers were searching for at least seven people in the water.

The vessel appears to have hit one of the supports of the Francis Scott Key Bridge, causing the roadway to break apart in several places and plunge into the water, according to a video posted on X, formerly known as Twitter.

The ship caught fire, and thick, black smoke billowed out of it.

“This is a dire emergency,” Kevin Cartwright, director of communications for the Baltimore Fire Department, told The Associated Press. “Our focus right now is trying to rescue and recover these people.”

Emergency responders were searching for at least seven people believed to be in the water, Cartwright said, though he said it’s too early to know how many people were affected. He called the collapse a “developing mass casualty event.”

He added that some cargo appeared to be dangling from the bridge, which spans the Patapsco River, a vital artery that along with the Port of Baltimore is a hub for shipping on the East Coast.

Opened in 1977, the bridge is named for the writer of “The Star-Spangled Banner.”

Agencies received emergency calls around 1.30am reporting that a ship leaving Baltimore had struck a column on the bridge, according to Cartwright.

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

From a vantage point near the entrance to the bridge, jagged remnants of its steel frame were visible protruding from the water, with the on-ramp ending abruptly where the span once began.

The ship is called “Dali," according to Cartwright. A vessel by that name was headed from Baltimore to Colombo, Sri Lanka, as its final destination, according to Marine Traffic and Vessel Finder. The ship was flying under a Singapore flag, WTOP radio station reported, citing Petty Officer Matthew West from the Coast Guard in Baltimore.

Mayor Brandon Scott and Baltimore County Executive Johnny Olszewski Jr. posted that emergency personnel were responding and rescue efforts were underway.

“All lanes closed both directions for incident on I-695 Key Bridge. Traffic is being detoured,” the Maryland Transportation Authority posted on X.

In 2001, a freight train carrying hazardous materials derailed in a tunnel in downtown Baltimore and caught fire, spewing black smoke into surrounding neighbourhoods and forcing officials to temporarily close all major roads into the city. (AP)