Six workers were missing and presumed dead from a bridge that collapsed in Baltimore Harbor early on Tuesday after a massive cargo ship crippled by a power loss rammed into the structure, forcing the closure of one of the busiest ports on the U.S. Eastern Seaboard.

With dive teams facing increasingly treacherous conditions in the darkened, wreckage-strewn waters, active search-and-rescue operations were suspended about 18 hours after the accident, U.S. Coast Guard and Maryland State Police officials said, Reuters reported. 

Coast Guard Rear Admiral Shannon Gilreath said there was no hope of finding the missing workers alive due to the frigid water and the length of time elapsed since the accident.

State Police Colonel Roland Butler said authorities hoped to return divers to the water after sunrise on Wednesday in an effort to recover the workers' remains.

The Singapore-flagged container vessel named Dali, heading out of Baltimore Harbor bound for Sri Lanka, plowed into a support pylon of the Francis Scott Key Bridge over the mouth of the Patapsco River at about 1:30 a.m. (0530 GMT).

A trestled section of the 1.6-mile (2.57 km) span almost immediately crumpled into the icy water, sending vehicles and people into the river.

Rescuers pulled two survivors to safety, one of whom was hospitalized. They and the six missing were part of a work crew filling potholes on the road surface of the bridge, officials said earlier.