Authorities are trying to rescue at least seven people.
Around 1.30am local time on Tuesday, a large vessel crashed into the bridge, catching on fire before sinking and causing multiple vehicles to fall into the water below, according to a video posted on X, formerly known as Twitter.
"All lanes closed both directions for incident on I-695 Key Bridge. Traffic is being detoured," the Maryland Transportation Authority posted on X.
Mayor Brandon M Scott and Baltimore County executive Johnny Olszewski Jr posted that emergency personnel were responding and rescue efforts were underway.
Emergency responders were searching for at least seven people believed to be in the water, Kevin Cartwright, director of communications for the Baltimore Fire Department, told the Associated Press.
He said agencies received 911 calls around 1.30am local time reporting a vessel travelling 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's too early to know how many people were affected but called the collapse a "developing mass casualty event".
Cartwright said it appears 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.
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