The ship saga of the Baltimore bridge crash has concluded as the Dali sailed out of Baltimore's port, nearly three months after a deadly crash that killed six people. 

The cargo ship left the US city on Monday, nearly three months after it lost power and crashed into one of the Francis Scott Key Bridge's supporting columns and caused the bridge to collapse.

The 300 metre long Dali started moving shortly before 8:30am escorted by four tugboats, with a crew of 22 and six salvage experts aboard, the US Coast Guard said. 

The coast guard is shepherding the cargo ship as it makes its way to offload roughly 1,500 containers at a container terminal in Portsmouth, 174 kilometres south.

Repairs and salvage works will be carried out on the vessel, which has been out of action since the crash.

The Dali lost power and propulsion early on the morning of March 26 shortly after leaving Baltimore's port, when it crashed into one of the bridge's supporting columns, killing six construction workers.

It was refloated and guided back to port in May, after being stuck in the bridge's wreckage for almost two months with a giant steel truss draped across its front half.  

Investigations by the US Transport Safety Board showed the ship lost power twice before it left port the morning of the crash, and then later again, moments before veering off course into the bridge. 

The cause of the power outages is yet to be determined. 

Baltimore's port was partially closed for months following the crash, with thousands of jobs impacted and the restoration of shipping traffic made a priority. 

The bridge will be rebuilt, with state officials saying they hope construction will be finished by 2028. 

AP/ABC