Demolition crews were cutting into portions of the Francis Scott Key Bridge's collapsed truss Sunday and an enormous container ship remained trapped underneath the rubble, five days after the collision that killed six people, forced a shutdown of the Port of Baltimore and halted shipping traffic through one of the nation's most crucial ports.

The Unified Command, including the Coast Guard and Maryland officials, said Sunday that two massive cranes were "actively working on scene" while another land-based crane was positioned to help offload and process the wreckage at a nearby industrial port. Three dive teams were surveying submerged sections of the wreckage in the murky waters of the Patapsco River.

"The removed wreckage is being lifted and transferred to a barge as daylight allows," the Unified Command said in a news release Sunday.

The Unified Command is also coordinating with Baltimore Gas and Electric to reduce the pressure of the underwater natural gas pipeline, which "spans the width of the channel and runs under the incident site."

Four bridge workers remained missing and presumed dead following Tuesday's catastrophe, when the Singapore-flagged container ship Dali, more than three football fields long, slammed into the bridge. Two other victims were recovered from the site Wednesday.

In recent days, hazardous weather conditions and the collapse wreckage have made it impossible for divers to continue recovery operations for the four remaining bodies, according to Maryland Gov. Wes Moore.

Tom Perez, senior adviser and assistant to President Joe Biden, said Sunday that the president's plans to visit the area were still being worked out. He called the salvage operation a "Herculean undertaking" vital to minimizing the national supply-chain disruption caused by the collapse.

"The Port of Baltimore will be back," Perez told MSNBC's "The Weekend." "The president has said this. We're going to move heaven and earth to make sure we rebuild the bridge, we clear out the debris as soon as possible, so that we can minimize these disruptions."

Temporary channel to be established for essential vessels

Crews are preparing to establish a temporary, alternate channel on the northeast side of the main channel for commercially essential vessels, according to the Unified Command.

“This will mark an important first step along the road to reopening the port of Baltimore,” Capt. David O’Connell, federal on-scene coordinator for the Key Bridge response, said in a statement Sunday. “By opening this alternate route, we will support the flow of marine traffic into Baltimore.”

The temporary channel is part of a "phased approach" to opening the main channel, the Unified Command said. It will be marked with aids to navigation and will have a depth of 11 feet, a 264-foot horizontal clearance, and a vertical clearance of 96 feet.

The 2,000-yard safety zone around the Francis Scott Key Bridge site remains in effect to protect personnel, vessels, and the marine environment, according to the Unified Command.

No timeline for removal of bridge rubble and ship

Transportation Secretary Pete Buttigieg said Sunday that the Army Corps of Engineers doesn't want to speculate on a timeline for repairs until damage to the underwater infrastructure can be fully assessed. After that a clearer picture of the supply chain issues will emerge, he said.

"What we do know is that we need to get this port back open as soon as possible, deal with the supply-chain applications in the meantime and get that bridge back up as soon as possible and deal with the traffic implications," Buttigieg on MSNBC's "Velshi."

Gov. Moore calls for 'speedy' investigation, accountability

Moore on Sunday stressed the need for a thorough investigation into the cause of the disaster and for accountability. The ship's operators made a mayday call moments before the crash saying the container ship had lost power.

The National Transportation Safety Board said its probe will include a study of information from the ship's black boxes.

"There needs to be an ongoing investigation as to what happened," Moore said on "Fox News Sunday." "I want that investigation to be speedy. And for anyone who needs to be held accountable to be held accountable."

The port handles more cars, heavy trucks and agriculture equipment than any other port "inside this country," making its reopening a "national imperative," he said.

"Not because anyone is trying to do Maryland a favor," Moore said. "It’s because the national economy relies on the port of Baltimore being up and running."

The governor also urged Congress to pass the federal funding needed for rebuilding the bridge and port economy. The Biden administration approved $60 million in initial emergency aid on Thursday to assist clean-up operations and help reopen the port, which has been closed since the collapse.

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22-member Dali crew remains aboard the battered ship

The 22-member crew of the Dali, made up of Indian nationals, has remained on board since the Tuesday incident. They monitored engineering spaces and will "appropriately respond to any emergency on board," Coast Guard spokesperson Cynthia Oldham told USA TODAY. The ship and its cargo of 4,679 containers were headed for Sri Lanka from Baltimore, a journey that would have taken about four weeks, so the crew has supplies to last that long. 

The ship's manager, Synergy Marine Group, said its emergency response team was on the ground in Baltimore and coordinating with authorities on all stages of recovery and remediation efforts.

"The ship managers have activated their mental health team to provide trauma counseling for crew members feeling distressed, and that service will continue," Synergy said in a statement.

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Temporary channel could expedite cleanup, shipping

Moore said Saturday that a section of the bridge's steel superstructure north of the crash site would be cut up and lifted by crane onto a barge and removed. A temporary channel can then be opened to allow some ships to access the area and "accelerate our recovery." He did not provide a timeline but warned that "it's not going to take hours, it's not going to take days."

A section of the bridge's superstructure remains across the bow of the Dali that lost power before hitting the bridge. It was not clear when the ship would be moved, he said, adding that it was damaged but that its hull remained intact.

Baker says he was among last to cross bridge before disaster

Maryland baker Larry Desantis says be believes he was one of the last people to flee the bridge in the moments before its devastating collapse. Desantis works at Herman's bakery in Dundalk, about 3 miles from the bridge. He told ABC News he drove over the bridge daily for 16 years, and drove over it at about 1:27 a.m. on Tuesday. A barge slammed into the bridge at 1:29 a.m.

"If I had been one minute later, I wouldn’t be here," Desantis said.

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He said he and a coworker often chat for a few minutes after work, but they didn't on Tuesday night.

"If we had done that, I may not be here today," he said.

Contributing: Reuters