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BALTIMORE — A cargo ship lost power and rammed into a major bridge in Baltimore early Tuesday, destroying the span in a matter of seconds and plunging it into the river in a terrifying collapse that could disrupt a vital shipping port for months. Six people were missing and presumed dead.

The ship’s crew issued a mayday call moments before the crash took down the Francis Scott Key Bridge, enabling authorities to limit vehicle traffic on the span, Maryland’s governor said.

The ship struck one of the bridge’s supports, causing the structure to collapse like a toy. The vessel caught fire, and thick, black smoke billowed out of it.

With the ship barreling toward the bridge at “a very, very rapid speed,” authorities had just enough time to stop cars from coming over the bridge, Maryland Gov. Wes Moore said.

“These people are heroes,” Moore said. “They saved lives last night.”

The crash happened in the middle of the night, long before the busy morning commute on the bridge that stretches 1.6 miles (2.6 km) and was used by 12 million vehicles last year.

The six people still unaccounted for were part of a construction crew filling potholes on the bridge, said Paul Wiedefeld, the state’s transportation secretary.

A senior executive at the company that employed the construction workers said Tuesday afternoon that they were presumed dead, given the water’s depth and the length of time since the crash.

Jeffrey Pritzker, executive vice president of Brawner Builders, said the crew was working in the middle of the bridge when it came apart. No bodies have been recovered.

“This was so completely unforeseen,” Pritzker said. “We don’t know what else to say. We take such great pride in safety, and we have cones and signs and lights and barriers and flaggers. But we never foresaw that the bridge would collapse.”

Rescuers pulled two people out of the water. One person was treated at a hospital and discharged hours later.

Multiple vehicles also went into the water, although authorities did not believe anyone was inside.

“It looked like something out of an action movie,” said Baltimore Mayor Brandon Scott, calling it “an unthinkable tragedy.”

A police dispatcher put out a call just before the collapse saying a ship had lost its steering and asked officers to stop all traffic, according to Maryland Transportation Authority first responder radio traffic obtained from the Broadcastify.com archive.

One officer who stopped traffic radioed that he was going to drive onto the bridge to alert the construction crew. But seconds later, a frantic officer said: “The whole bridge just fell down. Start, start whoever, everybody … the whole bridge just collapsed.”

On a separate radio channel for maintenance and construction workers, someone said officers were stopping traffic because a ship had lost steering. There was no follow-up order to evacuate, and 30 seconds later the bridge collapsed and the channel went silent.

From 1960 to 2015, there were 35 major bridge collapses worldwide due to ship or barge collision, according to the World Association for Waterborne Transport Infrastructure.

The collapse is almost sure to create a logistical nightmare for months, if not years, along the East Coast, shutting down ship traffic at the Port of Baltimore, a major shipping hub. The accident will also snarl cargo and commuter traffic.

“Losing this bridge will devastate the entire area, as well as the entire East Coast,” Maryland state Sen. Johnny Ray Salling said.

Highway signs as far south as Virginia warned drivers of delays associated with the bridge.

Authorities said sonar had detected vehicles in the water, which is about 50 feet (15 meters) deep. The water temperature was about 47 degrees Fahrenheit (8 degrees Celsius) before dawn Tuesday, according to a buoy that collects data for the National Oceanic and Atmospheric Administration.

Synergy Marine Group — which manages the ship, called the Dali — confirmed the vessel hit a pillar of the bridge at about 1:30 a.m. while in control of one or more pilots, who are local specialists who help guide vessels safely into ports. The ship is owned by Grace Ocean Private Ltd.

Synergy said all crew members and the two pilots on board were accounted for, and there were no reports of any injuries.

The ship was moving at 8 knots, roughly 9 mph (14.8 kph), the governor said.

Jagged remnants of the bridge could be seen jutting up from the water’s surface. The on-ramp ended abruptly where the span once began.

Donald Heinbuch, a retired chief with Baltimore’s fire department, said he was startled awake by a deep rumbling that shook his house for several seconds. “It felt like an earthquake,” he said.

He drove to the river’s edge and couldn’t believe what he saw.

“The ship was there, and the bridge was in the water, like it was blown up,” he said.

The bridge spans the Patapsco River at the entrance to a busy harbor, which leads to the Chesapeake Bay and Atlantic Ocean. Opened in 1977, the bridge is named for the writer of “The Star-Spangled Banner.”

Wiedefeld said all vessel traffic into and out of the port would be suspended until further notice, though the facility was still open to trucks.

President Joe Biden said he planned to travel to Baltimore “as quickly as I can” and that he intends for the federal government to pick up the entire cost of rebuilding the bridge.

“This is going to take some time,” Biden said. “The people of Baltimore can count on us, though, to stick with them at every step of the way until the port is reopened and the bridge is rebuilt.”

The FBI was on the scene and said there was no credible information to suggest terrorism.

The Dali was headed from Baltimore to Colombo, Sri Lanka, and flying under a Singapore flag, according to data from Marine Traffic. The container ship is about 985 feet (300 meters) long and about 157 feet (48 meters) wide, according to the website.

Inspectors found a problem with the Dali’s machinery in June, but a more recent examination did not identify any deficiencies, according to the shipping information system Equasis.

Danish shipping giant Maersk said it had chartered the vessel. No Maersk crew and personnel were on board.

Last year, the Port of Baltimore handled a record 52.3 million tons of foreign cargo worth $80 billion, according to the state.

The head of a supply chain management company said Americans should expect shortages of goods from the effect of the collapse on ocean container shipping and East Coast trucking.

“It’s not just the port of Baltimore that’s going to be impacted,” said Ryan Petersen, CEO of Flexport.

The collapse, though, is not likely to hurt worldwide trade because Baltimore is not a major port for container vessels, but its facilities are more important when it comes to goods such as farm equipment and autos, said Judah Levine, head of research for global freight booking platform Freightos.