Efforts to locate the missing submersible are ongoing, and the "complex" search covers an area larger than the state of Connecticut, Coast Guard Capt. Jamie Frederick said at a news conference Tuesday.

Crews are scouring the ocean 900 miles east of Cape Cod and 400 miles south of St. John's, Canada, he said.

The missing five-person crew on the submersible has about 41 hours of oxygen left, Frederick noted.

"We will do everything in our power to effect a rescue," Frederick said.

"We have a group of our nation's best experts," he said, and once the sub is located, "those experts will be looking at what the next course of action is" to rescue the crew members.

"Our thoughts and prayers are with the crew and their families and their loved ones," Frederick added.

In 2000, Dr. Michael Guillen, then an ABC News correspondent, was filming from the wreck of the Titanic when his vessel became trapped in the propeller.

"When we collided with the propeller, and I started seeing those big chunks of metal raining down on us … the first reaction I had was, 'This can't be happening,'" he recalled to ABC News on Tuesday.

"We got caught by this underwater turn and just drove us right into the blades," Guillen said.

"This voice came into my head and said, you know, 'This is how it's going to end for you,'" he recalled. "I'll never forget those words."

"I'm very aware of what these poor souls on board the ship the Titan are experiencing," he said. "I am just heartbroken about it."

At the request of French President Emmanuel Macron, a French ship named Atalante is diverting to the area of the missing submissive and should reach the area Wednesday night.

The ship has an exploration robot that can dive up to 4,000 meters, according to a spokesman for France's Ifremer Institute.

Per Wimmer, an explorer and global financier, told ABC News he was "shocked" and "horrified" to hear of the missing submersible.

"It felt very personal. … I've been wanting to go down to the Titanic for more than a decade," Wimmer said.

He estimated that there's been between 150 and 200 missions to the Titanic.

There "are very, very few submersibles in the whole world that can go down to the depth of Titanic, which sits at 3,800 meters, or about 12,000 feet," Wimmer said. "It's very deep -- most submersibles can go down to about 1,000 meters."

"It's a race against time, because there's only 96 hours of oxygen on board. And after that, if you haven't reached the surface, you starve of oxygen," he said.

"Our best hope at the moment is that the safety mechanism will be activated," he said. "It is supposed to be able to float to the surface, little by little, and then they can open the hatch and hopefully get out again. That is the only hope we have, because you do not have enough time to get another submersible that can go that deep."

-ABC News' Dom Proto

Samad Dawood, the brother of Shahzada Dawood, one of the passengers who died in the submersible, said losing his brother and nephew, Suleman Dawood, is heartbreaking.

"This is beyond what you could ever imagine in terms of the kind of hardships and struggle that we've had. I think what we've seen is enormous tragedy and devastation and a lot of emotions. Obviously we were hoping to hear some good news about the rescue and them coming back. It was heartbreaking to find out that that's not the case," Samad Dawood told ABC News.

Samad Dawood said his brother had a strong sense of adventure and curiosity about the world.

"He was always the kind of person who has this incredible love for the world," Samad Dawood said.

"He inspired us curiosity. And he was a guy who just wanted to go out there, experience what the world had to offer, even though he he himself pushed himself to do it. So they made adventures to go to Antarctica, to go to Greenland and to go to Africa and go to the rapids," Samad Dawood said.

This sense of adventure was passed on to Shahzada Dawood's son, 19-year-old Suleman Dawood, who was also in the submersible. Suleman Dawood had traveled to all seven continents, according to Samad Dawood.

"He was so filled with humbleness and gratitude," Samad Dawood said.

"We're deeply grateful for all the support and the love and the effort that the people have made, working tireless nights being optimistic in giving a sense of hope, giving that transparency to us. But obviously we were devastated as a family ... that we couldn't get them back safe," Samad Dawood said.

-ABC News' Octavio Cadenas, Dr. Jennifer Ashton and Victor Ordonez