A major bridge in Baltimore, Maryland, collapsed early Tuesday after a Singapore-flagged container ship struck a pillar of the decades-old bridge, leaving six people presumed dead, according to state authorities.

The 289-meter-long freighter, named Dali, struck the Francis Scott Key Bridge at around 1:30 a.m., resulting in its collapse into the Patapsco River. US officials reported no indication of a terrorist attack.

At the time of the collapse, there were at least eight construction workers conducting repair work on the bridge, with six of them listed as unaccounted for. After hours of a search and rescue operation, the Coast Guard transitioned to a recovery operation to locate the bodies of the missing.

Coast Guard Rear Adm. Shannon Gilreath said that due to the length of time spent on the search and the water temperature, the missing are thought to be dead.

"We do not believe that we're going to find any of these individuals still alive," he told reporters. "We are going to suspend the active search and rescue efforts ... We are transitioning to a different phase."

President Joe Biden said there was no sign of an "intentional" act linked to the tragedy.

"Everything so far indicates that this was a terrible accident," Biden said in a livestreamed speech, pledging to send "all the federal resources" needed to rebuild the bridge. "At this time, we have no other indication, no other reason to believe there was any intentional act here."

Maryland Gov. Wes Moore gave the same assessment earlier.

"The preliminary investigation points to an accident. We haven't seen any credible evidence of a terrorist attack," he told reporters.

"Our administration is working closely with leaders from all levels of government and society to respond to this crisis and not just by addressing the immediate aftermath but also by building a state that is more resilient and a state that is safer," he added.

The Maryland authorities confirmed that the crew on the cargo ship notified authorities of a power outage.

Before the collision, the ship issued a Mayday call, a distress signal that allowed officials to control traffic going into the bridge, according to the Maryland governor.

"We're thankful that between the mayday and the collapse, that we had officials who were able to begin to stop the flow of traffic so more cars were not on the bridge," Moore was quoted by CNN as saying.

Footage of the collapse on YouTube showed the freighter ramming into a pillar of the bridge with its collapse happening in less than a minute shortly thereafter.

Maryland authorities said that the ill-fated bridge was "fully up to code" while an early analysis suggests the collapse was an accident.

Named after the author of the American national anthem, "The Star-Spangled Banner," the 2.6-kilometer-long steel arch bridge opened in 1977. It has since served as the outermost crossing of Baltimore Harbor.

The collapse happened less than 30 minutes after the cargo ship started its weekslong trip to Sri Lanka, according to The New York Times. The ship was built by Hyundai Heavy Industries, a South Korean shipbuilder, in 2015. (Yonhap)