The US Coast Guard launched a search and rescue operation Monday to locate a submarine that went missing during an expedition taking tourists to the wreckage of the Titanic, CNN partner CTV News reported.

The group conducting the trip, Oceangate Expeditions, said it is "exploring and mobilizing all options to bring the crew back safely."

"Our entire focus is on the crewmembers in the submersible and their families. We are deeply thankful for the extensive assistance we have received from several government agencies and deep sea companies in our efforts to reestablish contact with the submersible," the group said. "We are working toward the safe return of the crewmembers."

CNN has reached out to the Boston Coastguard and authorities in Newfoundland, Canada.

The Titanic infamously hit an iceberg on its maiden voyage and sank in the North Atlantic Ocean in April 1912, killing over 1,500 people. The wreckage of the Titanic, discovered in 1985, sits in two parts at the bottom of the ocean nearly 13,000 feet below the surface southeast of Newfoundland.

More recently, costly private tours have been offered to tourists, allowing people to see the wreck up close.

An archived version of OceanGate's website, accessible via the Internet Archive's Wayback Machine, lays out what passengers can expect on the $250,000 trip.

"Follow in Jacques Cousteau's footsteps and become an underwater explorer — beginning with a dive to the wreck of the RMS Titanic. This is your chance to step outside of everyday life and discover something truly extraordinary," the website said. "Become one of the few to see the Titanic with your own eyes."

The eight-day expedition is based out of St. John's, Newfoundland, Canada, with a maximum of six people. The trip begins with a 400-nautical-mile journey to the wreck site.

There, up to five people, including a pilot, a "content expert" and three paying passengers, board the submersible named "Titan" and descend to the bottom of the ocean.

"Once the submersible is launched you will begin to see alienlike lifeforms whizz by the viewport as you sink deeper and deeper into the ocean. The descent takes approximately two hours but it feels like the blink of an eye," the website said.

This is a developing story and will be updated.