A new underground tunnel, which is far below the sea level, has been discovered in the world’s largest cave Son Doong in the central province of Quang Binh.

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

The research diving trip made by a team including British divers, who were members of the rescue team saving the Thai football team trapped in Thailand's Tham Luang Cave last year.

The trip was expected to prove that the passage connected Son Doong and the Thung Cave, which is a cave of the same type laying 600m away.

The divers said they found a hole inside the passage and that hole leads to a tunnel.

The team plans to return to Vietnam next year to try to link the tunnel to another cave near Son Doong.-VNA