A container ship rests against wreckage of the Francis Scott Key Bridge as night falls on Tuesday, as seen from Sparrows Point, Md.

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A container ship rests against wreckage of the Francis Scott Key Bridge as night falls on Tuesday, as seen from Sparrows Point, Md. / AP

Rescue efforts have turned to recovery in the tangled wreckage of the Francis Scott Key Bridge in Baltimore.

Authorities are working to recover the bodies of six workers who are presumed dead after a cargo ship struck the bridge early Tuesday morning, sending the structure — and anyone on it — plunging into the frigid Patapsco River.

Federal investigators are trying to understand what led to the bridge's collapse, as the region braces for a long and costly rebuilding process.

Here's what we know:

Who was involved?

Authorities say eight people fell into the Patapsco River below after the collision. Two were rescued, with one person in critical condition while the other person refused medical treatment, Baltimore Mayor Brandon Scott said.

The six people who are still unaccounted for are believed to be construction workers who were repairing potholes on the bridge.

"Those are my friends, my co-workers," Jesus Campos told member station WYPR. "I could have been there like them," he said.

Campos said he was scheduled to work on the bridge the following morning. The men were from Mexico, Honduras, Guatemala and El Salvador, and all between 30 and 45 years old, said Campos.

The U.S. Coast Guard suspended its search and rescue efforts late Tuesday night and said the six people are presumed to be dead, given the amount of time that had passed since the collapse and the temperature of the water. They resumed recovery efforts Wednesday morning.

Twenty-two people were aboard the ship and are all accounted for, said Synergy Marine Group, the company that manages the ship.

How did it happen?

The Dali, a nearly 1,000-foot-long container ship registered in Singapore, appeared to lose power as it began moving toward the bridge at about 8 knots, or 9.2 miles per hour.

Those onboard issued a mayday, said Maryland Gov. Wes Moore, which gave authorities time to stop the flow of traffic on the bridge.

The Dali crashed into one of the bridge's support pillars, and parts of the structure came down immediately, at about 1:30 a.m.

Federal investigators are seeking to understand why the ship drifted so far off course and crashed into the bridge.

The chair of the National Transportation Safety Board, Jennifer Homendy, said investigators have recovered the voyage data recorder, which is similar to the black box recorders found on airplanes.

"We do have the data recorder," Homendy said in an interview with CNN on Wednesday morning. "We've sent that back to our lab to evaluate and begin to develop a timeline of events that led up to the strike on the bridge, and we hope to have that information to share with the public later today."

Investigators will also examine the ship's records and safety history, Homendy said, as well as the construction and structure of the bridge.

NTSB investigators typically take weeks or even months before releasing preliminary reports.

So far, law enforcement officials say there is no indication that the incident was intentional — but that hasn't stopped conspiracy theories from spreading on social media.

Cranes stand over shipping containers at the Port of Newark on Tuesday as seen from Bayonne, N.J. Supply chains at ports up and down the East Coast are expected to be affected after a cargo ship hit and collapsed the Francis Scott Key Bridge in Baltimore.

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Cranes stand over shipping containers at the Port of Newark on Tuesday as seen from Bayonne, N.J. Supply chains at ports up and down the East Coast are expected to be affected after a cargo ship hit and collapsed the Francis Scott Key Bridge in Baltimore. / Getty Images

Have there been any previous incidents involving the ship or bridge?

The ship has had 27 previous inspections. In 2016, it sustained significant damage to its hull after hitting a dock while leaving a port in Antwerp, Belgium. Last year, the ship was found to have a problem with "propulsion and auxiliary machinery," according to Equasis, a maritime safety site.

The Key Bridge, which is four lanes, 1.6 miles long and carries about 11.3 million vehicles a year, was fully up to code and had no structural issues, Moore said.

Will the bridge be rebuilt?

Federal and local authorities immediately vowed to rebuild the bridge, but they cautioned that the process would not be fast or cheap.

"There is no exact precedent for this," Transportation Secretary Pete Buttigieg told NPR's Morning Edition.

Buttigieg declined to give a timeline of how long reconstruction might take, though he noted the original bridge took five years to build. And Buttigieg underscored the importance of reopening the shipping channel as quickly as possible.

"This port is the top vehicle handling port in the United States," Buttigieg said. "We can't wait for the bridge work to be complete to see that channel reopened. There are vessels that are stuck inside right now and there's an enormous amount of traffic that goes through there. That's really important to the entire economy."

President Biden said he wants the federal government to pay for the entire cost of reconstructing the bridge.

"We're gonna get it up and running again as soon as possible," Biden said on Tuesday. "Fifteen-thousand jobs depend on that port, and we're gonna do everything we can to protect those jobs and help those workers."

What we don't know

Authorities have not yet released any information about the pilot or captain of the ship, or why it seemed to lose power. The NTSB, the FBI and state officials are investigating.

The economic impact is also unknown, but it's likely to be huge.

A large portion of the Baltimore port remains closed indefinitely. That port is just a fraction of the size of large ones in the U.S. like Newark or Long Beach, Calif. But it plays an outsized role in auto imports and is economically significant to Maryland and the region.

About $80 billion worth of cargo goes through the Port of Baltimore each year, including about 850,000 cars and trucks. The port also provides 15,000 jobs, with about $3.3 billion in personal income, $2.6 billion in business revenue and $400 million in tax revenue, according to the state.