Jose Montalvo, of South Carolina, was buried by the concrete girder, authorities said.
A second worker, whose name wasn't released, was critically injured and was being treated at New Hanover Regional Medical Center.
The state departments of Transportation and Labor were investigating the incident Wednesday afternoon. There was no word on the cause of the collapse.
Work began on the 4.52-mile bridge across the Intracoastal Waterway in August 2007 and is scheduled for completion in December 2009.