The Francis Scott Key bridge has collapsed in the American city of Baltimore after a container ship rammed into the bridge, with at least six people unaccounted for.

Nine News US Correspondent, Jonathan Kearsley, said it’s been a “very difficult day” for the community in Baltimore.

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One of the world’s leading bridge designers, Ian Firth, told Ross and Russ “when these things happen, we learn lessons”.

“It’s an absolutely tragic situation,” Mr Firth said.

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Image: 9News