Here’s what we know about the catastrophe:

Why did the bridge collapse?

Shortly before 1:30 a.m. Tuesday, a Singaporean-flagged container vessel called DALI struck one of the 47-year-old bridge’s pillars, officials said.

The local pilot of the ship did “everything that he could have done” to slow the ship and keep it from drifting toward the bridge, Clay Diamond, executive director and general counsel of the American Pilots Association, told CNN.

“Just minutes before the bridge, there was a total blackout on the ship, meaning that the ship lost engine power and electrical power, it was a complete blackout,” Diamond said.

The pilot then did “everything that he could have done” to both slow the ship down and keep it from drifting to the right, toward the bridge, he added.

The pilot quickly gave a string of orders, calling for a hard rudder to port –- as far left as possible -– and for an anchor to be dropped.

Video of the 95,000 gross ton ship approaching the bridge shows lights on the vessel going off then turning back on – likely due to an emergency generator activating after the initial blackout – but the ship’s engines never got running again, according to Diamond.

The Maritime and Port Authority of Singapore said in a written statement that dropping anchor is part of emergency protocol and confirmed the DALI was not under engine power.

“As a result (of the momentary loss of power), it was unable to maintain the desired heading and collided with the Francis Scott Key bridge,” the statement said, attributing the information to the ship management company, Synergy Marine Pte Ltd.

Footage of the crash also showed the 984-foot long vessel, which had been chartered to carry cargo by Danish shipping giant Maersk, was in the wrong part of the channel as it approached the bridge.

The ship crashed into a pillar toward one side of the bridge instead of crossing under the middle of the bridge, where the clearance is highest.

“If you look at it, it’s off center of where it should be,” Maryland Transportation Secretary Paul J. Wiedefeld told CNN.

“Obviously, it should be in the main channel, which is under that main span.”

Rescue mission for six missing turns into recovery operation

Six people who were on the bridge at the time of collapse are missing and feared dead, officials said at separate news conferences. The victims include Mexican and Guatemalan nationals.

Rafael Laveaga, the Chief of the Consular Section of the Mexican Embassy in Washington who spoke to reporters near the scene Tuesday, confirmed the victims include Mexican nationals but did not say how many are Mexican.

“We know our people are involved,” Laveaga said. “It was a crew who was repairing parts of the potholes on the bridge, and they’re the ones who are going to build the bridge again – the Latinos.”

The Ministry of Foreign Affairs in Guatemala identified one of the construction workers on the bridge as a 26-year-old originally from San Luis, Petén, and the other as a 35-year-old from Camotán, Chiquimula.

Laveaga said it’s too early to determine the nationalities for all the victims and that it’s a priority to be in very close contact with the authorities.

“Accidents happen and it was a very unfortunate tragedy,” he said.

All six are construction workers who were filling potholes on the surface of the bridge when the ship crashed, Wiedefeld said. The construction work “had nothing to do with a structural issue at all,” Wiedefeld said.

Coast Guard Rear Adm. Shannon Gilreath told reporters the water temperature, the length of time since the incident and the results of the extensive search have led them to switch from rescue to recovery mode.

“At this point we do not believe that we are going to find any of these individuals still alive,” he said at a news conference.

Two of the missing workers were from Guatemala, officials at the Ministry of Foreign Affairs in that country said.

Two other people who were on the bridge were rescued from the Patapsco River, Baltimore City Fire Chief James Wallace said Tuesday morning. One of them was not injured, and the other was taken to a trauma center in “very serious condition,” he said.

By Tuesday afternoon, the hospitalized patient had been discharged, the University of Maryland Medical Center said.

Wallace told CNN on Tuesday afternoon that at least 50 personnel and eight dive teams were part of the search.

Sonar technology detected cars submerged in the water after the crash, but there are no known victims in those cars, Wiedefeld said. It’s believed the cars belonged to the construction workers.

No one aboard the DALI was injured, according to Synergy Group.

Only construction worker vehicles were on the structure, officials say

While many of the 30,000 to 35,000 cars and trucks that traversed the Key Bridge daily can be rerouted through the two nearby tunnels, that will cause traffic delays. And hazardous materials are prohibited from tunnels so they will be diverted on a longer detour.

According to the Johns Hopkins University’s “An Engineers Guide to Baltimore,” the Key bridge combined “the behaviors of an arch, truss and cantilever. With no expansion joints, this bridge is the second longest continuous steel truss bridge in the United States.”

Conditions too dangerous for search

Search operations have shut down for the night due to dangerous conditions, Wallace said on CNN’s “Anderson Cooper 360.”

Wallace said there is a lot of instability with steel sections of the bridge that are hanging from other pieces of unsupported debris. There is a lot of “steel superstructure” on the bow of the Dali that is “very unstable,” as well as containers hanging off the vessel, he added.

Wallace said they are also concerned about the structural stability of what remains of the bridge.

The deeper you go in the river, the lower the visibility gets, Wallace said, adding that water depths in the area under the bridge vary from 40 feet to more than 60 feet. The deeper divers go, the colder the temperatures they encounter, and the visibility is zero, he added.

Wallace said when crews arrived Tuesday morning, the surface water temperatures of the Patapsco River were about 47 degrees with an air temperature of 44-45 degrees.

Swimmers without floatation can survive in water temperatures of 40 to 50 degrees for about 30 to 60 minutes, according to the University of Minnesota. With the aid of floatation devices, the likely survival time is about two to three hours.

Coast Guard searches for potentially hazardous materials

The US Coast Guard is examining more than a dozen damaged containers, some with potentially hazardous materials, that were aboard the container ship that crashed into the bridge, according to a US government document obtained by CNN and a US official familiar with the matter.

Thirteen damaged containers, “some with Centers for Disease Control and Prevention [CDC] and/or hazardous materials [HAZMAT] contents,” are being examined by an elite Coast Guard team, according to an unclassified memo from the federal Cybersecurity and Infrastructure Security Agency distributed to non-government organizations and critical infrastructure operators on Tuesday evening.

A Coast Guard team trained in dealing with hazardous materials is going through the ship’s manifest to determine what was on board and what, if any, health risk, there might be from that material, the official said.

About 1.8 million gallons of “marine diesel spill potential” from the crashed ship is also being monitored by federal officials, according to the memo. Estimates like that are the “worst case scenario,” the US official told CNN, adding “lots would have to go wrong now for all that fuel to spill.”

Still, first responders are taking precautions to minimize any potential fuel spill from the cargo ship. The 1.8 million gallons is “not an unusual amount of fuel for a ship of that size to carry,” the official told CNN.

Was this an accident or an intentional act?

There is no indication the ship’s crash and the bridge collapse were intentional, state and federal officials said.

Still, the FBI is on the scene. There are multiple reasons for that, former Deputy FBI Director Andrew McCabe said.

“The first is because when you have an event like this that calls for a massive response (and) resources, all of the local law enforcement entities, federal entities, whoever’s in the area, because of mutual aid agreements, will show up and contribute whatever resources they have,” McCabe told CNN.

For example, the FBI has “very experienced dive teams” that can help with the search, McCabe said.

Second, the FBI can help confirm whether the disaster was intentional. “They will look through all their intelligence holdings to see if there’s any chatter talking about plans or targeting, about locations like this, to see if there’s anything in the background that we should have been aware of and watching for,” McCabe said.

“Obviously, we’ve heard from numerous officials that that is not the case at this point.”

What happens next?

While crews scramble to find the missing, the National Transportation Safety Board will lead the investigation into the accident, NTSB chair Jennifer Homendy said.

“We have a team of 24 on scene,” Homendy said Tuesday afternoon.

The team includes experts in nautical operations, who will collect information on vessel operations, safety history, the ship’s owner, the operator, company policy and any safety management system.

“We have a team here that is getting the recorders. We also have a highway safety team … including structural engineers, bridge experts who will be here and are continuing to come in,” Homendy said.

President Joe Biden said he’s committed to helping rebuild the bridge as soon as possible.

“It’s my intention that the federal government will pay for the entire cost of reconstructing that bridge. And I expect the Congress to support my effort,” the president said.

“15,000 jobs depend on that port, and we’re gonna do everything we can to protect those jobs and help those workers,” Biden said.

“It’s one of the most important elements for the economy in the Northeast and the quality of life.”

US Transportation Secretary Pete Buttigieg said there will be a major and protracted impact to supply chains and the path to “normalcy” will be difficult.

“It will not be quick. It will not be inexpensive. But we will rebuild together,” the transportation secretary said. “It’s too soon to offer estimates on what it will take to clear the channel and reopen the port.”