In reacting to news of the OceanGate submersible implosion, "Titanic" director James Cameron told ABC News that he was "struck by the similarity of the Titanic disaster itself, where the captain was repeatedly warned about ice ahead of his ship and yet he steamed at full speed into an ice field."

Cameron, who has built his own submersible, was critical of OceanGate's use of a carbon-fiber hull, calling it "fundamentally flawed."

OceanGate CEO Stockton Rush, who was among the five passengers killed on the submersible, had previously said he believed a sub made with carbon fiber would have a better strength-to-buoyancy ratio than titanium.

"Titanic" director James Cameron, who has explored the wreckage site himself, called the implosion "quite surreal" and noted that one of the passengers killed, Paul-Henri Nargeolet, was a friend of his.

"For him to have died tragically in this way is almost impossible for me to process," Cameron told ABC News Thursday.

Coast Guard officials said a remote-operated vehicle found the tail cone of the Titan submersible about 1,600 feet from the bow of the Titanic Thursday morning.

Additional debris found was "consistent with the catastrophic loss of the pressure chamber," Rear Adm. John Mauger, the First Coast Guard District commander, said during a press briefing.

The passengers' families were immediately notified.

Five major pieces of debris were found, including the nose cone, officials said.

The debris indicates there was a "catastrophic implosion" of the vessel, Mauger said.

It's too early to tell when the implosion occurred, officials said.

"This is an incredibly unforgiving environment down there on the seafloor," Mauger said.

All five aboard the missing submersible are believed to be lost amid a search for the vessel, OceanGate said.

"We now believe that our CEO Stockton Rush, Shahzada Dawood and his son Suleman Dawood, Hamish Harding, and Paul-Henri Nargeolet, have sadly been lost," OceanGate said in a statement.

"These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world’s oceans," the statement continued. "Our hearts are with these five souls and every member of their families during this tragic time. We grieve the loss of life and joy they brought to everyone they knew."

As crews scour the Atlantic Ocean for the missing submersible, the U.S. Coast Guard said it's searching in the area where underwater noise was detected.

The unidentified noise was detected Tuesday night and Wednesday morning.

The data on the noise was sent to the U.S. Navy to be examined, according to the Coast Guard.

"We have to remain optimistic and hopeful when we're in a search and rescue mission," Capt. Jamie Frederick, the First Coast Guard District response coordinator, said at a press conference on Wednesday afternoon.

The deep-sea vessel submerged on Sunday morning with five people aboard and a 96-hour oxygen supply, according to the Coast Guard. That amount of breathable air is forecast to run out on Thursday morning.

When asked about the search becoming a recovery mission, Frederick told reporters: "We're not there yet."