Crews have begun to cut and remove the first pieces of the Francis Scott Key Bridge in Baltimore, a week after the collision killed six people and triggered a collapse. 

A section of the bridge's steel superstructure north of the site of the crash was lifted onto a barge by a crane and then removed. 

In a media address on Sunday local time, Maryland Governor Wes Moore said the complete removal of the bridge would take time but the current goal is to create safe passage for tug boats and barges through the waterway. 

The clearing of a channel for more boats will then allow more vessels in to begin recovery works and reopen passage to the essential port. 

"An operation that is this complex and this unprecedented you need to be able to plan for every single moment and this work is going to take time and we are going to continually assess and reassess," he said. 

"First we need to focus on recovery, we need to clear the channel and open vessel traffic to the port," he said. 

Mr Moore said retrieval of the remaining bodies of the six people who are believed to have plunged to their deaths from the bridge has not been possible.

"Conditions in the water make it unsafe," he said.

"Not just wind and weather make it unsafe for rescue divers but we're talking about debris, wreckage and pieces of bridge in the water."

Colonel Roland Butler of the Maryland State Police said rescue teams remain on standby to retrieve remaining bodies when it is safe to do so. 

Container ship Dali, which still has 22 person crew of Indian nationals on board,  will then be removed. 

The crew are currently monitoring engineering spaces and are on standby for further emergencies until the ship's removal. 

The vessel is tangled in 3,000 to 4,000 tonnes of debris.

Most of its containers remain intact, but some were torn open or knocked away by the falling debris.