Astaldi Canada, the contractor carrying out work at the Muskrat Falls construction site, says Tuesday's shutdown was caused by a load of steel that fell the equivalent of four storeys.
"A load of steel was being hoisted by a crane and as a result of a rigging failure, the load fell to the ground from an approximate height of 40 feet," Matthew Pike, Astaldi's manager of external relations, said in a statement.
Work at the site immediately stopped.
No one was injured, although Nalcor Energy, which is supervising the Muskrat Falls project, described the case as a "serious safety incident."
Work at the site will resume Thursday. Workers took part in a mandatory two-hour safety session, and will also be debriefed on Tuesday's near-miss.