Baltimore's Francis Scott Key Bridge collapse could cost insurers billions of dollars in claims, analysts say, with one putting it at as much as $4 billion, which would make the tragedy a record shipping insurance loss.

Six people are still missing after a collision with a Singapore-flagged container ship destroyed the landmark bridge on Tuesday, forcing the closure of one of the busiest U.S. ports.

With little clarity on when the Port of Baltimore would re-open, insurers and analysts are now assessing the likely losses borne by underwriters across several product lines including property, cargo, marine, liability, trade credit and contingent business interruption.

"Depending on the length of the blockage and the nature of the business interruption coverage for the Port of Baltimore, insured losses could total between $2 billion and $4 billion," said Marcos Alvarez, managing director for global insurance ratings at Morningstar DBRS. That would surpass the record insured losses of the Costa Concordia luxury cruise liner disaster in 2012, he said.