EXPLAINER-Why did the Baltimore bridge collapse and what do we know about the ship?

(Adds details on container ship and Baltimore port)

By Lisa Shumaker

March 26 (Reuters) - Baltimore's Francis Scott Key Bridge collapsed early on Tuesday after a container ship smashed into the four-lane span, plunging cars into the river.

WHAT HAPPENED IN BALTIMORE?

At 1:27 a.m. ET (0527 GMT), a container ship named the Dali was sailing down the Patapsco River when it struck a pylon of the bridge, crumpling almost the entire structure into the water. There was no indication of terrorism, police said.

ARE THERE ANY CASUALTIES?

The headlights of vehicles could be seen on the bridge as it crashed into the water and the ship caught fire.

Baltimore officials said several vehicles plunged into the water. As many as seven people could be in the river. At least one person was seriously injured.

WHAT DO WE KNOW ABOUT THE SHIP THAT WAS INVOLVED?

The Dali was leaving Baltimore en route to Colombo, Sri Lanka. All 22 crew, including two pilots on board, have been accounted for and there were no injuries, the ship's manager, Synergy Marine Group said.

The registered owner of the Singapore-flagged ship is Grace Ocean Pte Ltd, LSEG data show. The ship is 948 feet (289 meters) long and was stacked high with containers.

The ship can hold up to 10,000 twenty-foot equivalent unit, or TEU, a measure of cargo capacity. It was carrying 4,679 TEU.

WHAT DO WE KNOW ABOUT THE BRIDGE THAT COLLAPSED? The Francis Scott Key bridge is a four-lane structure that sits 185 feet (56 meters) above the river. It opened in 1977 and crosses the Patapsco River, where U.S. national anthem author Francis Scott Key wrote the "Star Spangled Banner" in 1814 after witnessing the British defeat at the Battle of Baltimore and the British bombing of Fort McHenry.

The bridge carries 11.3 million vehicles a year, according to the Maryland Transportation Authority, on the I-695 highway that circles Baltimore, also known as the Baltimore Beltway.

HOW WILL THE BRIDGE COLLAPSE IMPACT THE BALTIMORE PORT? Traffic was suspended at the port after the collision. It is one of the smallest container ports on the Northeastern seaboard, handling about a tenth of the volume that passes through the Port of New York and New Jersey. The flow of containers to Baltimore can likely be redistributed to bigger ports, said container shipping expert Lars Jensen.

(Writing by Lisa Shumaker; Editing by Daniel Wallis)