A crew of Swedish divers scavenging the Baltic Sea for treasures has shared new images of their baffling discovery — a large disc-shaped object settled on the seabed.

In a press release that sounds as if it were inspired by the underwater sci-fi film The Abyss, the unidentified object is described as circular, with rounded sides and rugged edges.

Deep-sea treasure hunters claim to have discovered an anomaly at the bottom of the Baltic Sea, described as similar in size and shape to the fictional Millennium Falcon from Star Wars. (Ocean Explorer team/Scanpix/Sipa Press)

"The object had an egg-shaped hole leading into it from the top, as an opening," the release said, drawing comparisons from several media outlets to the fictional Millennium Falcon spacecraft featured in Star Wars.

Stefan Hogeborn, one of the divers in the expedition, said he was perplexed by the shape and structure of the circular object, which is about 60 metres in diameter and rises three to four metres from the seabed. That's roughly the size of a jumbo jet.

Adding to the mystery, the object was also reported to have a 400-metre-long trail leading away from it, similar in appearance to skid marks. Another smaller disc-shaped object was found nearby, also with apparent drag lines about the same length.

The Ocean Explorer team that first laid claim to the find last year also described stone circle formations resembling "small fireplaces" and covered in a residue resembling soot.

"I can’t explain what we saw, and I went down there to answer questions, but I came up with even more questions," Hogeborn said in a statement Friday, noting that stones don't normally burn.

'Strangest' experience in diving career

In the release, Peter Lindberg, one of the founders of the Ocean Explorer team, called the finding "the strangest thing I have ever experienced as a professional diver." Lindberg had said in a previous interview his initial thought when he encountered the object was that the team had discovered a sunken UFO.

'This is no game. But the truth will be reported shortly'—Dennis Aasberg, Ocean Explorer team

The new photos released Friday lacked perspective and were apparently taken during the Ocean Explorer team's most recent dive. The team said its mission was to return to the same secret location between Sweden and Finland this week, armed with more sophisticated sonar gear, in order to further their investigations and take samples.

Coverage surrounding the find has ignited speculation from some conspiracy theorists about the possibility of either a sunken UFO or a USO (unidentified submerged object). Other commentators on social media, including paranormal and Area 51 theorists on Twitter, have questioned whether the mysterious build-up to the Baltic investigation is a hoax or viral marketing gag.

Some messages posted to the Ocean Explorer Facebook page expressed similar sentiments.

Dennis Aasberg, a lead diver with the Ocean Explorer team, did little to suppress anticipation for an announcement.

He teased the discovery this week on Facebook, writing: "Everything is top secret now…because of the risks…hope you all understand this is no game. But the truth will be reported shortly."

The Ocean Explorer team gained notoriety in 1998, after divers surfaced bearing crates of vintage champagne from a First World War-era ship sunk in 1916. The haul of 4,000 bottles of champagne and 68 bottles of cognac was valued at about $3,000 a bottle.