(Reuters) -A submarine on a tourism expedition to explore the wreckage of the Titanic has gone missing off the coast of southeastern Canada, according to the private company that operates the vessel.

OceanGate Expeditions said in a brief statement on Monday that it was "mobilizing all options" to rescue those on board the vessel. It was not immediately clear how many people were missing.

The U.S. Coast Guard did not immediately respond to requests for comment. Media reports said the Coast Guard has launched search-and-rescue operations.

"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," OceanGate said in a statement.

The company is currently operating its fifth Titanic "mission" of 2023, according to its website, which was scheduled to start last week and finish on Thursday.

The expedition, which costs $250,000 per person, starts in St. John's, Newfoundland, before heading out approximately 400 miles into the Atlantic to the wreckage site, according to OceanGate's website.

In order to visit the wreck, passengers climb inside Titan, a five-person submersible, which takes about two hours to descend to the Titanic.

The British passenger ship famously sunk in 1912 on its maiden voyage after striking an iceberg, killing more than 1,500 people. The story has been immortalized in non-fiction and fiction books as well as the 1997 blockbuster movie "Titanic".

(Reporting by Joseph Ax, Njuwa Maina and Kanishka Singh; Additional reporting by Ismail Shakil; Editing by Doina Chiacu)