The bodies of two people have been recovered from a red pickup truck, which was submerged under the water where the Baltimore bridge collapsed.
Eight construction workers were on the bridge when a ship struck it, plunging them into the waters below.
Two of the workers were rescued on the day, but the search continues for the other four - all presumed dead.
Salvage crews are working to address hazardous materials and accident investigators are on the scene.
Four of the six victims of the bridge collapse have been named so far.
At a press conference on Wednesday, Maryland State Police identified Alejandro Hernandez Fuentes, 35, and Dorlian Ronial Castillo Cabrera, 26, as the two workers recovered by divers from inside the truck. Mr Fuentes is originally from Mexico and Mr Cabrera is from Guatemala.
But divers are no longer able to safely navigate the waters because of concrete and debris found in the river, police said. They are now using sonar scans and believe that vehicles that may contain other bodies are "encased in superstructure and concrete" that came down from the bridge, an official said.
Two other missing victims, who are presumed dead, have also been named: Miguel Luna, originally from El Salvador, and Maynor Suazo Sandoval, a Honduran citizen.
Mexico's Ministry of Foreign Affairs said earlier that two of its citizens were presumed dead - one of whom is now identified as Mr Fuentes - while another was rescued from the water.
One person who was in hospital after being pulled out of the water was released, officials said late Wednesday.
First responders spent hours on Tuesday searching the waters of the Patapsco River for the six construction workers, who were working on potholes on the bridge around 01:30 (05:30 GMT) when the ship crashed into the bridge. The US Coast Guard called off the search around sunset, saying cold water temperatures and hours gone by meant the workers were presumed dead.
Officials have pledged to find the bodies of the men for their relatives.
"We've got to give these families closure," Mr Moore told reporters on Wednesday, adding that air, land and water resources have been devoted to the search of the victims.
"My promise to them is this: I will devote every single resource to make sure that you receive closure," he said.
But the operation has been challenging, Coast Guard Vice Admiral Peter Gautier said on Wednesday.
Divers have been swimming in chilly waters with metal debris from the bridge that fell in the river.
The cargo vessel itself is stable but has over 1.5m gallons of fuel oil and lube oil on board, Mr Gautier said.
Roughly 4,700 cargo containers were also on board, including 56 that contained hazardous materials.
"The Coast Guard has moved aggressively to board the vessel, and we have teams on board," Mr Gautier said.
The US Navy plans to use barges with heavy lift cranes - some can carry as much as 1,000 tonnes - to remove parts of the bridge that fell in the water.
Investigations into what went wrong on the ship will be crucial, marine specialist Jim Bellingham told the BBC.
"An enormous advantage is that the ship didn't sink so they'll get access to bridge records and hopefully recordings of what was going on," he said.
Officials are hoping that a data recorder they took from the ship overnight will provide more information.
The Dali was headed toward Sri Lanka when it lost power all of a sudden and issued a distress call before crashing into the Baltimore bridge.
Officials say the bridge collapse at a key port could pose a risk to global supply chains and the US economy.
Maryland Governor Wes Moore said that 8,000 jobs could be affected by the bridge collapse and called the incident a "global crisis".
"The national economy and global economy depends on the port," he said, noting that $80bn (£63.4bn) of cargo moved through there last year.
Paul Wiedefeld, Secretary of the Maryland Department of Transportation, stressed that replacing the bridge will not be a fast process, but he promised at Wednesday's press conference that officials are working to "come up with a design for the replacement of that bridge as quickly as possible to get the port back up and the community back up and running".
Experts say Key Bridge's collapse could lead to losses of up to $15m (£11.8m) per day, until the shipping lane is reopened.
US Senator Ben Cardin of Mary said he was confident "thanks to the Biden administration" the state would get the necessary resources to recover and begin work on a replacement bridge.
"Our top priority is to get the shipping lane open because of the impact it has on our country and the global supply chain," he said.
Investigators are also hoping to determine whether dirty fuel played a role in the deadly crash. Maritime experts say contaminated fuel can cause a ship to black out as it creates problems with a vessel's main power generators.
BBC