Hanoi (VNA) – A new underground tunnel, which isfar below the sea level, has been discovered in the world’s largest cave SonDoong in the central province of Quang Binh.

The information was disclosed at an international pressconference on the latest diving expedition inside the cave in Hanoi on April 9.

The research diving trip made by a team including Britishdivers Richard Stanton, John Volanthen, Jason Mallison and Chris Jewell, whowere members of the rescue team saving the Thai football team trapped inThailand's Tham Luang Cave last year.

The research began this month and the divers started work atthe end of the river inside Son Doong and went further into a water passage.The trip was expected to prove that the passage connected Son Doong and theThung Cave, which is a cave of the same type laying 600m away.

The expectation was based on results made by the BritishCave Research Association’s team, who were the first to explore Son Doong,following a survey they did in 2010.

However, the passage was actually not in a straight line andit went deeper underground, said Volanthen at the media briefing. He said thedivers found a hole inside the passage and that hole leads to a tunnel.

Unfortunately, normal air compressors that the divers hadduring the research trip were unable to keep them safe for further diving andthe divers had to end their first visit to the tunnel.

“The actual depth of the tunnel could be 100m or more. Imanaged to reach a depth of 77m and couldn’t go further due to the failure ofequipment,” said Mallison.

However, according to Howard Limbert, Mallison’s remarkshelped prove that Son Doong did not end where the river poured into thepassage, but expanded into the underground tunnel. Limbert was a member of theBritish caving team who first explored the cave. Today he is the technicalmanager of Oxalis Adventure Tours, the sole tour provider into the giant cave.

“We will take a second research trip to the tunnel nextyear,” said Nguyen Chau A, Oxalis director. He revealed at the press briefingthat at first the diving expedition in Son Doong was initiated as an award forthe heroism of Tham Luang’s British divers but later turned out to be thetoughest task.

Howard appraised the early success in finding the tunnel anddescribed the diving as one of the most “difficult and challenging tasks”.-VNA