VIDEO: Francis Scott Key Bridge in Baltimore collapses, several cars plummet into the Patapsco River

BALTIMORE, Md. - Early Tuesday morning, the Francis Scott Key Bridge in Baltimore collapsed into the Patapsco River. A large boat was headed for the bridge when it appeared to lose power and struck one of the supporting pillars, initiating the fall.

A Baltimore City Fire Department Spokesperson told the Associated Press that rescue crews went from searching for seven people to now 20 people in the river after several cars fell in the water. Two people have already been rescued as of early Tuesday morning. Officials said that underwater drones, sonar and infrared surveillance tools had confirmed there were several cars in the river.

Representatives from the Ada County Fire Department, Baltimore County Fire Department, Maryland Department, U.S. Coast Guard and the Maryland Transportation Authority Police are responding to the incident. First responders are calling this a "mass casualty incident."

The bridge serves as the outermost crossing of the Baltimore Harbor and is an essential link of Baltimore Beltway (Interstate-695). The bridge had four lanes and was about a mile and a half long.

According to the Maryland Transportation Authority, Sunday marked the 46th anniversary of the bridge opening to traffic as the final link of the I-695. Construction of the bridge began in 1972 and is believed to span the site of where Francis Scott Key witnessed the bombardment of Fort McHenry in September 1814, the inspiration behind Key's song, "Star Spangled Banner."

The Maryland Transportation Authority encourages people to use I-95 or I-895 as alternate travel routes.