A container ship smashed into a four-lane bridge in the U.S. port of Baltimore in darkness on Tuesday, causing it to collapse and sending cars and people plunging into the river below.

Rescuers pulled out two survivors, one in a "very serious condition," and were searching for more in the Patapsco River after huge spans of the 1.6-mile (2.57 km) Francis Scott Key Bridge crumpled into the water.

The ship "lost propulsion" as it was leaving port, and crew on board notified Maryland officials they had lost control of the vessel, ABC News reported, citing an unclassified U.S. intelligence report.

Baltimore officials said at least seven vehicles plunged into the water but could not give an exact figure.

Kevin Cartwright, the spokesperson for Baltimore City Fire Department, earlier told Reuters that as many as 20 people could be in the river along with "numerous vehicles, and possibly a tractor-trailer or a vehicle as large as a tractor-trailer, (that) went into the river."

"This is a mass-casualty, multi-agency event," he said. "This operation is going to extend for many days."

Tuesday's disaster may be the worst U.S. bridge collapse since 2007 when the I-35W bridge in Minneapolis collapsed into the Mississippi River, killing 13.

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