The US Coast Guard has opened a temporary, alternate channel for vessels involved in the clearing of debris at the site of the collapsed Francis Scott Key Bridge in Baltimore, part of a phased approach to opening the main channel leading to the vital port, officials said.

Crews have begun the complicated work of removing steel and concrete after the bridge’s deadly collapse into the Patapsco River following a freighter collision last week.

On Sunday, dive teams surveyed parts of the bridge and checked the ship, and workers used blowtorches to cut above-water parts of the twisted steel superstructure.

Officials said the temporary channel is open only to vessels that are helping with the clean-up effort.

Authorities believe four workers plunged to their deaths in the collapse. Recovery of their bodies is a key part of the ongoing salvage operation.

The channel will have a controlling depth of 11ft (more than 3m), a horizontal clearance of 264ft (80m) and a vertical clearance of 96ft (29m), officials said. A video released on Sunday showed the Coast Guard dropping buoys in the water.

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

On Monday, the Small Business Administration is opening a centre in Dundalk, Maryland, to help small businesses get loans to help them with losses caused by the disruption from the bridge collapse.

The bridge fell as the crew of the cargo ship Dali lost power and control on March 26. They called in a mayday, which allowed just enough time for police to stop vehicles from getting on the bridge, but not enough time to get a crew of eight workers off the structure.

Two workers survived, two bodies were found in a submerged pick-up, and four more men are presumed dead. Weather conditions and the tangled debris underwater have made it too dangerous for divers to search for their bodies.

The Dali is managed by Synergy Marine Group and owned by Grace Ocean Private Ltd.

Danish shipping giant Maersk chartered the Dali, which was on its way out of port when it lost power and hit one of the bridge’s support columns.

Along with clearing the shipping channel to reopen the port, officials are trying to determine how to rebuild the major bridge, which was completed in 1977 and carried Interstate 695 around south-east Baltimore and was central to the city’s centuries of maritime culture.

Congress is expected to consider aid packages to help people who lose jobs or businesses because of the prolonged closure of the Port of Baltimore. The port handles more cars and farm equipment than any other US facility.