The director and deep-sea explorer James Cameron points to flaws in the Titan submersible’s design.

“We’ve never had an accident like this,” James Cameron, the Oscar-winning director of “Titanic,” said on Thursday.

Mr. Cameron, an expert in submersibles, has dived dozens of times to the ship’s deteriorating hulk and once plunged in a tiny craft of his own design to the bottom of the planet’s deepest recess.

In an interview, Mr. Cameron called the presumed loss of five lives aboard the Titan submersible from the company OceanGate like nothing anyone involved in private ocean exploration had ever seen.

“There’ve never been fatalities at this kind of depth and certainly no implosions,” he said.

An implosion in the deep sea happens when the crushing pressures of the abyss cause a hollow object to collapse violently inward. If the object is big enough to hold five people, Mr. Cameron said in an interview, “it’s going to be an extremely violent event — like 10 cases of dynamite going off.”

In 2012, Mr. Cameron designed and piloted an experimental submersible into a region in the Pacific Ocean called the Challenger Deep. Mr. Cameron had not sought certification of the vessel’s safety by organizations in the maritime industry that provide such services to numerous companies.

“We did that knowingly” because the craft was experimental and its mission scientific, Mr. Cameron said. “I would never design a vehicle to take passengers and not have it certified.”

Mr. Cameron strongly criticized Stockton Rush, the OceanGate chief executive who piloted the submersible when it disappeared Sunday, for never getting his tourist submersible certified as safe. He noted that Mr. Rush called certification an impediment to innovation.

“I agree in principle,” Mr. Cameron said. “But you can’t take that stance when you’re putting paying customers into your submersible — when you have innocent guests who trust you and your statements” about vehicle safety.

As a design weakness in the Titan submersible and a possible cautionary sign to its passengers, Mr. Cameron cited its construction with carbon-fiber composites. The materials are used widely in the aerospace industry because they weigh much less than steel or aluminum, yet pound for pound are stronger and stiffer.

The problem, Mr. Cameron said, is that a carbon-fiber composite has “no strength in compression”— which happens as an undersea vehicle plunges ever deeper into the abyss and faces soaring increases in water pressure. “It’s not what it’s designed for.”

The company, he added, used sensors in the hull of the Titan to assess the status of the carbon-fiber composite hull. In its promotional material, OceanGate pointed to the sensors as an innovative feature for “hull health monitoring.” Early this year, an academic expert described the system as providing the pilot “with enough time to arrest the descent and safely return to surface.”

In contrast to the company, Mr. Cameron called it “a warning system” to let the submersible’s pilot know if “the hull is getting ready to implode.”

Mr. Cameron said the sensor network on the sub’s hull was an inadequate solution to a design he saw as intrinsically flawed.

“It’s not like a light coming on when the oil in your car is low,” he said of the network of hull sensors. “This is different.”