The cargo ship Dali sits in the water after running into and collapsing the Francis Scott Key Bridge in Baltimore, Maryland. Photo: AFP
A major search and rescue operation is under way to find six construction workers believed to be on a Baltimore bridge when it collapsed after being hit by a fully-laden container ship overnight.
The four-lane Francis Scott Key Bridge crumpled into the frigid waters of the harbour and Patapsco River about 1.30am local time.
The BBC has reported that local construction crews were fixing pot holes on the bridge at the time it collapsed.
At least six people were unaccounted for. Two were rescued from the water, one in a serious condition.
Divers were among the search crews and Baltimore fire officials said vehicles had been detected in the water by sonar, the BBC said.
Jesus Campos speaks about his coworkers who were working on the night shift while repairing the Francis Scott Key Bridge at the time of its collapse. Photo: AFP
'I could have been there'
Jesus Campos, who works for Brawner Builders, told media gathered near the scene that he was waiting for news of his six coworkers.
Local public radio station WYPR Baltimore reported Campos was scheduled to work the morning shift.
"Those are my friends, my coworkers, I am sad… I could have been there like them," he said.
Brawner Builders had not yet confirmed whether or not the missing workers were their employees.
'Unspeakable tragedy'
Baltimore Mayor Brandon Scott said it was an "unspeakable tragedy".
The focus was on the search and rescue efforts, he said.
"Right now this is about the lives of these individuals we are still searching for.
"This is about the lives and the families who are deeply impacted."
Maryland Governor Wes Moore told media it was an "active" search and rescue operation.
He said he had been spending time with the families of those missing and he thanked the first responders.
US National Transportation Safety Board chair Jennifer Homendy. Photo: AFP
The National Transportation Safety Board chair Jennifer Homendy extended her deepest sympathies to those affected by the event.
She told a media conference NTSB would lead the investigation into what happened.
"Our deepest sympathies go out to families, loved ones, and others who have been affected. I'm going to get questions on fatalities and injuries which I'm not going to answer... I will refer you to local authorities on all of that information. What I can tell you is that a search and rescue is still underway so we are very hopeful."
Homendy said NTSB staff arrived on site early in the morning and were beginning to investigate while allowing the Coastguard to continue its search and rescue.