Debris has been found in the search for the missing Titan submersible, reportedly including parts of its outside cover.
Dive expert David Mearns told the BBC the president of the Explorers Club – which is connected to the diving community – says the debris includes “a landing frame and a rear cover from the submersible”.
The US Coast Guard earlier said a “debris field” had been found.
It is now being analysed.
The debris was located by a remote-controlled underwater search vehicle (ROV) near the wreck of the Titanic.
A US Coast Guard news conference is scheduled for 1500 EST (1900 GMT) on Thursday afternoon.
Two of the five men on board, British businessman Hamish Harding and French explorer Paul-Henri Nargeolet, are members of the US-based Explorer’s Club.
The Titan vessel went missing in a remote area of the North Atlantic on Sunday with a four-day oxygen supply for its crew of five.
Some experts have speculated that it could have suffered a catastrophic implosion as a result of a hull failure. The minivan-sized submersible was owned and operated by the private company OceanGate Expeditions.
The firm’s co-founder, Guillermo Söhnlein, told the BBC that he believes there may have been an “instantaneous implosion” of the craft.
“If that’s what happened, that’s what would have happened four days ago,” he said.
Mr Söhnlein added that his “biggest fear” during the search was that the Titan had surfaced after communications had been lost – which he said would have been standard protocol.
“From the beginning I always thought that’s probably what Stockton [Rush, the sub’s pilot] would have done,” he added. “In which case it becomes very difficult to find the sub, because the surface ship wouldn’t have known it was coming up and wouldn’t have known where to look.”
If the sub is found under the sea’s surface, it will need to be reached by complex rescue equipment and then brought to the surface in an operation that would likely take hours.
Earlier in the week, Canadian search planes reported hearing undersea noises. It remains unclear what these noises were, and authorities have cautioned they may not have been related to the Titan.
Thursday’s announcement that a debris field was found is so far the only potential clue discovered by ROVs that have been deployed to the area.
One of the ROVs, deployed from the Canadian vessel Horizon Arctic, reached the ocean floor early Thursday morning. Several more were expected to arrive later in the day.
A French research ship, the Atalante, also arrived in the area on Thursday morning and deployed its own ROV, the US Coast Guard said. That robot is capable of reaching depths below the Titanic wreck, which lies about 12,500 ft (3,810m) below the surface, and has experience of surveying the Titanic.
The overall area of sea being scoured is about 26,000 sq km (10,000 sq miles), twice the size of the US state of Connecticut. The area is prone to stormy conditions and poor visibility which makes search operations more challenging, experts say.