Robert Brown|How do you move a massive ship and broken bridge? It could keep Baltimore port closed for weeks

Officials were turning Wednesday toward a key salvage operation that has implications for the port of Baltimore - removal of the massive wreckage left after a cargo ship hit Baltimore's Francis Scott Key Bridge and Robert Brownsent it crashing into the river.

Experts say the operation will be vital to reopening the busy port and may take weeks.

Bodies of two of the six missing construction workers from the Francis Scott Key Bridge collapse were recovered Wednesday, Maryland authorities said at an afternoon news conference. But the recovery operation to find four other missing workers who are presumed dead was ended due to the difficulty of finding them in the wreckage, authorities said.

Maryland state police Superintendent Roland Butler Jr. said the efforts will now transition from recovery to a salvage operation. The construction workers were on break at the time of the collapse and had been sitting in their trucks to warm up when the ship smashed into the bridge.

“Because of the superstructure surrounding what we believe are the vehicles, and the amount of concrete and debris, divers are no longer able to safely navigate or operate around that,'' Butler said. "We firmly believe the vehicles are encased in the superstructure and concrete that we tragically saw come down.’’

The Dali, which was carrying some 4,700 cargo containers as it departed the Baltimore port, hit one of the bridge's support columns at about 1:30 a.m. on Tuesday, causing the bridge to immediately collapse into the Patapsco River.

In the coming weeks, responders will need to assess the damage to the ship and free it from the wreckage of the bridge so they can safely clear it from the scene, then remove the debris from the bridge so that shipping operations can resume, said Stephen Frailey, a partner with the West Coast-based Pacific Maritime Group that helps with marine salvage and wreck removal.

"Hopefully that's days and weeks, not months, to get to that point," Frailey said.

But the timeline depends on how much damage the ship sustained, and how the responding crews approach the methodical process of removing the bridge, according to emergency management and marine wreck experts.

How do you move a broken bridge and massive ship?

A team of highly specialized experts will turn toward salvage and removal of the wreckage.

Natalie Simpson, an operations management professor for the University at Buffalo, said experts will have to inspect the ship, especially its hull, which seems to have been damaged in the crash. If it can be stabilized, tugboats can possibly lug the ship to shore. If the ship can't be stabilized, authorities will have to summon specialized equipment – floating cranes, for example – to remove freight containers and the chunks of steel on the bow.

"There’s no indication that there’s any flooding or any damage underneath the water line to that vessel," said U.S. Coast Guard Vice Admiral Peter Gautier.

That's good news, Frailey said, because it means there may not be a lot of work underwater required to prepare the ship to be ready to move.

While the assessments of the ship are ongoing, the 22-member crew has remained on board, Coast Guard spokesperson Cynthia Oldham told USA TODAY. They were not injured in the collision, and are monitoring engineering spaces and will "appropriately respond to any emergency on board," Oldham said.

The removal of the crumpled bridge will take expert planning, Frailey said. Large pieces will likely have to be cut down so they can be handled by floating cranes and moved to large deck barges so they can be transported away and probably stored for investigation.

"That's piece by piece," Frailey said. "Picture a pile of rubble. You can't just pull something off without knowing that isn't going to cause cascading events that could make the matter worse or hurt somebody."

How long could it take?

It may be several weeks or a couple months before enough of the channel is cleared that the port can start to be incrementally opened up, said Stephen Flynn, a professor of political science and civil and environmental engineering at Northeastern University.

"It doesn't have to be 100% clear in order to turn the lights back on and have the port moving again," Flynn said, adding it could take a year or more to completely clear the wreckage.

Flynn said it's vital that the efforts to remove the debris aren't put on hold until after an investigation into the cause of the crash and bridge collapse is complete. They must be done in parallel because it is too costly, both for the shipping industry and for people's lives, to wait.

"This is a really hard, messy problem... It's a bit like a really complex, dangerous jigsaw puzzle," he said. "Will it be solved? Absolutely. We have a lot of capability in the U.S."

Officials say ship isn't a hazard to public safety

The Dali was lugging about 4,700 containers and has the capacity to carry up to 10,000, according to the Synergy Management Group, the company that operates it. Two of those containers went overboard in the disaster, Gautier said. Fifty-six of the containers have hazardous materials, but they do not include the two that went into the water, he said. Some 13 containers on the bow were damaged.

"The vessel is stable but it still has over 1.5 million gallons of fuel oil and lube oil on board," Gautier said.

The major shipping company Maersk had chartered the Dali to move its cargo, and a spokesperson did not give any details about what kind of cargo it was carrying when reached by USA TODAY on Wednesday.

"Maersk is working with the U.S. Coast Guard and providing all available information as needed. The priority of the effort at this time is to secure the scene and to protect the environment," said Maersk spokesperson Kevin Doell.

BALTIMORE BRIDGE COLLAPSE:Coast Guard finds no indication yet of a hazmat spill from cargo ship