"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."

A Royal Canadian Navy ship HMCS Glace Bay has been on scene since about 8 a.m. ET Thursday morning. The ship provides a medical team specializing in dive medicine and a six-person mobile hyperbaric recompression chamber, according to officials.

Canadian Coast Guard ships John Cabot, Ann Harvey and Terry Fox are on scene and ready to provide rescue equipment and personnel should assistance be required. A Royal Canadian Air Force CP-140 Aurora aircraft is also maintaining continuous on-scene support with additional aircrews and assets, according to officials.

-ABC News' Luke Barr

A senior U.S. Navy official confirmed to ABC News that an underwater acoustic detection system heard on Sunday what was likely the implosion of the Titan submersible. The information was immediately shared with the U.S. Coast Guard on Sunday and analysis continued afterwards.

"The U.S. Navy conducted an analysis of acoustic data and detected an anomaly consistent with an implosion or explosion in the general vicinity of where the Titan submersible was operating when communications were lost," the senior official told ABC News in a statement. "While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission."

According to the official, "This information was considered with the compilation of additional acoustic data provided by other partners and the decision was made to continue our mission as a search and rescue and make every effort to save the lives on board.”

Separately, a U.S. defense official said an analysis of the “banging” noises picked up by sonar buoys were not from the missing submersible but were either natural ocean sounds, biological noises or noises associated with the surface response vessels.

-ABC News' Luis Martinez