The disaster has forced the indefinite closure of the Port of Baltimore, one of the busiest on the U.S. Eastern Seaboard, and created a traffic quagmire for Baltimore and the surrounding region.

Rescuers have lost hope of finding more survivors of the Baltimore bridge collapse, the coast guard said, as efforts switched on Wednesday to looking for bodies of the missing and more answers to why a container ship smashed into the span.

Search divers were expected to return near dawn to the waters surrounding the twisted ruins of the bridge in Baltimore Harbor to search for six workers missing and now presumed dead.

The disaster has forced the indefinite closure of the Port of Baltimore, one of the busiest on the U.S. Eastern Seaboard, and created a traffic quagmire for Baltimore and the surrounding region.

As the odds of their survival vanished, the search for the missing workers was suspended on Tuesday evening, 18 hours after they were thrown from the fallen Francis Scott Key Bridge into the frigid waters at the mouth of the Patapsco River.

"We do not believe that we're going to find any of these individuals alive," Coast Guard Rear Admiral Shannon Gilreath said at a briefing.

Maryland State Police and U.S. Coast Guard officials said diminished visibility and increasingly treacherous currents in the wreckage-strewn channel made continued search efforts on the river too risky to continue overnight.

Starting at 6 a.m. (1000 GMT) on Wednesday, "we're hoping to put divers in the water and begin a more detailed search to do our very best to recover those six missing people," state police Colonel Roland Butler told reporters late on Tuesday.

It was unclear whether authorities also tried to alert the work crew ahead of the impact.

Maryland Governor Wes Moore said at a Tuesday news briefing the bridge was up to code with no known structural issues. There was no evidence of foul play, officials said.