BALTIMORE has sued the owner and operator of the container ship that decimated the iconic Francis Scott Key Bridge, killing six construction workers.

The mayor and city council filed the suit in the US District Court of Maryland on Monday to seek unspecified damages from Grace Ocean Pte Ltd, the Singaporean owner, and manager Synergy Marine Group, Reuters reported. They want the owners held fully liable via a jury trial.

The ship lost power and hit a bridge pylon in the early hours on March 26, collapsing the entire structure and plunging several workers into the icy depths of the Patapsco River. Two of the workers were rescued, while the bodies of four have been recovered. Two more are still missing and presumed dead.

The plaintiffs allege that the ship was experiencing an inconsistent power supply as it left port that night, making the decision to set sail criminally negligent.

In addition to loss of life, the destruction of a bridge that was a mainstay in the regional and national economy had caused the city's economic drivers to "grind to a halt", the suit alleges, according to Reuters.

"Today, the City filed its claim against the owners and managers of the Dali, in accordance with admiralty and maritime law", the Baltimore City Law Office said in a statement obtained by CBS affiliate WJZ-TV.

"The City is pursuing its legal claims against those responsible for the Key Bridge catastrophe to ensure that the City, its residents, and its businesses are adequately compensated for their losses. As this matter is now the subject of active litigation, we will reserve further comment for the appropriate judicial forum."

The suit also claims that crew members were incompetent and lax in carrying out their duties, WJZ reported.

A spokesperson for the two companies told Reuters it would be inappropriate to comment while the US Coast Guard and federal regulators are still investigating. The FBI has opened a criminal probe, as well.

The defendants already filed legal documents to try and limit their liability or limit any damages to the value of the ship and its estimated revenue, which would amount to about US$44 million, WJZ said.