Unanswered questions remain after New Jersey firefighters killed in raging blaze on European-made cargo ship

Investigators are searching for answers after two firefighters were killed and five more were injured while battling a raging blaze aboard a cargo ship docked in Newark, New Jersey.

It was the first time since 2007 that a Newark firefighter was killed on the job, according to city officials.

The blaze was still smoldering some 36 hours after it broke out on the massive vessel, according to Tom Wiker, president of Gallagher Marine Systems, which was hired by the ship's owner to extinguish the flames.

"The fire is going to burn for a couple more days probably," Wiker said during a press conference on Friday.

While the cause of the blaze remains under investigation, there is an indication the firefighters' equipment was incompatible with the European-made ship's fire suppression system, sources close to the probe told ABC News on Thursday. The firefighters weren't trained to handle blazes that take place on cargo boats, a source said.

The fire continues to burn "very hot," making the steel ship inaccessible to firefighters, so crews are trying to to cool it from the perimeter by dousing the vessel with water and keeping the flames contained toward the top deck, according to Gordon Lorenson, project manager at Donjon Marine, which provides marine support services.

Although the ship remains stable, it is currently "listing" to one side, mainly due to the amount of water being hosed on it, Lorenson said. Crews are monitoring the situation and working to bring the boat back to an "even keel" by pumping out water, he added.

"You can do all the training in the world and you're going to find something you've never seen before in a shipboard fire," Lorenson told reporters on Friday.

Firefighters were dispatched to the Port Newark Container Terminal on Wednesday at around 9:30 p.m. ET after receiving a report about multiple vehicles on fire aboard a 692-foot cargo ship named the Grande Costa D'Avorio. They managed to extinguish the main body of the blaze but the flames had extended to multiple levels of the vessel, according to city officials.

The United States Coast Guard also responded to the fire, describing the boat in a Twitter post as a "roll on/roll off vehicle cargo ship."

At 10:25 p.m., the firefighters called a "Mayday" after two of their own became trapped inside the burning vessel and were nowhere to be seen. That was followed by a second "Mayday" call 15 minutes later, city officials said.

Two Newark firefighters -- 45-year-old Augusta Acabou and 49-year-old Wayne Brooks -- were ultimately found early Thursday and subsequently taken to a hospital where they both died, according to city officials. New Jersey Gov. Phil Murphy ordered flags to be flown at half staff across the state on Friday to mourn the fallen firefighters.

"Augusto Acabou served as a firefighter for over 9 years and Wayne Brooks, Jr. served for over 16 years, with honorable devotion, remarkable courage, exceptional professionalism, loyalty, and commitment to the city of Newark and this state," Murphy said in a statement. "New Jersey has lost two courageous heroes who dedicated their lives to keeping our communities safe."

President Joe Biden called the families of the slain firefighters and offered his condolences, according to a White House official.

White House press secretary Karine Jean-Pierre said the president has been kept updated on the situation and the administration has been in touch with the Coast Guard and local authorities to coordinate on the response.

"We are going to continue to monitor the situation closely, this incident, and stand ready to provide as much assistance as needed to help contain the fire and get port operations back to normal," she said during Friday's press briefing.

Three other firefighters from the Newark Fire Department as well as two from the Elizabeth Fire Department were injured during the incident, according to city officials.

As of 5:20 a.m. on Thursday, the blaze was under control and firefighting operations were mostly completed, though crews were continuing to monitor the ship. The fire was contained in an area of the 11th and 12 floors of the vessel, which has a Halon fire suppression system, city officials said.

One of the issues encountered by the firefighters was that their two-and-a-half-inch fire hose lines weren't compatible with the boat's one-inch connections, a source close to the investigation told ABC News on Thursday. Instead, the firefighters were forced to use the fire hoses on the ship, which output less water and pressure than they were used to, the source said.

Firefighters were still trying to put out the lingering flames on Thursday night, both from the pier and from waterside. Crews were working to gain access to the upper decks of the ship, which is believed to be the primary source of the ongoing blaze, according to the Coast Guard.

On Friday morning, a sheen could be seen on the water around the boat.

The fire "spread significantly" on the vessel overnight, expanding down two levels -- from the 9th to the 7th floor -- and extending roughly 300 feet forward, according to the New Jersey governor. The firefighters currently battling the blaze are "all privately contracted by the ship's owner and have specialized training in marine firefighting," Murphy told reporters on Friday.

As of Friday evening around 10 p.m. ET, the fire was still burning on the upper decks.

Murphy noted that the boat is currently listing 3 degrees toward the dock, which is "a growing concern," since a 5 to 6 degree shift is considered "the danger zone."

"Due to the significant amount of debris on the ship, the normal outflow sprouts are clogged and water is not able to flow out at the rate it is able to flow in," he added. "Both the Coast Guard and a private marine company are poking holes through the hull to allow the trapped water to drain out. There is no timeline as to if or when the ship would reach the danger zone, as it remains to be seen how successful this operation will be."

Sailing under the Italian flag, the Grande Costa D'Avorio left the Port of Baltimore on Sunday and recently arrived in Newark. The vessel was built in 2011 and is operated by the Grimaldi Group, a Naples-based company that describes itself as Italy's largest ship-owning group.

The fire began as the boat's crew was completing cargo operations of loading automobiles on board. The crew immediately activated the ship's fire suppression procedures, while the local fire department was alerted, according to the Coast Guard.

The vessel is reportedly carrying 1,200 vehicles and 157 containers that were scheduled to be exported, none of which are electric cars or hazardous cargo, the Coast Guard said.

Newark firefighters are trained to battle blazes on cruise ships and other boats that contain living quarters but not ones that carry vehicles, according to Newark Fire Chief Rufus Jackson.

"This was definitely a unique fire for us," Jackson said during a press conference on Thursday.

ABC News' Victoria Arancio, Mark Crudele, Jessica Gorman, Karen Travers and Josh Margolin contributed to this report.