Multiple cars were sent into the water below, bringing the Coast Guard and emergency response teams to the scene along Interstate 695 at approximately 1:30 a.m., when a cargo ship struck a portion of the bridge.
Two people had been rescued as of 10:20 a.m., according to the Washington Post. At least six other construction workers remain unaccounted for, and another hospitalized, the news agency said.
Baltimore Mayor Brandon Scott declared a state of emergency at approximately 9:30 a.m.
The Baltimore Fire Department's communications director Kevin Cartwright said the incident was a "mass casualty event," CBS reports.
A livestream of the bridge showed lights of the Singaporean ship flickering in the Patapsco River moments before the crashing into the bridge, setting off an explosion.
Paul Wiedefeld, the Maryland State Transportation secretary, tells CNN workers were on the bridge doing concrete deck repair when it collapsed. A facility has been set up for their family members, he said.
Vehicles that plunged into the river were detected by sonar, Wallace tells CNN.
Members of the FBI were on scene for the investigation.
Click here to follow Daily Voice Lancaster and receive free news updates.