The move came after the American television network ABC (American Broadcasting Company) on May 13 made a live broadcast through the Good Morning America programme featuring En and Son Doong caves – secluded in the core area of the provincial UNESCO-recognised Phong Nha-Ke Bang National Park .

Howart said there is vast potential within the Ke Bang karst mountain and ventured that there might be a bigger or equally-sized cave to Son Doong – recognised as the world’s largest cave in 2009, according to Saigon Giai Phong (Saigon Liberated) newspaper.

Initial studies indicate that En cave – which is around two kilometres from Son Doong and the third biggest cave in the world, does not serve as an outlet for flood waters to drain from Son Doong cave, but as the waters do drain every flood season, there are assumptions about the existence of an undiscovered cavern system within the Ke Bang karst mountain.

The two-hour broadcasting from the ABC drew the attention of about 6 million subscribers and about 60 million others on the internet. This is the first live feed from an Asian country for Good Morning America – the number one morning show in the US.

To prepare for the programme, ABC sent a 15-member crew and more than a tonne in specialised equipment to Vietnam . A 32-second trailer of the programme, which used modern fly cams to take aerial shots, was screened online last week, attracting viewers.

Son Doong Cave , which scientists believe was formed 2-5 million years ago, was first discovered in the Phong Nha-Ke Bang National Park by a local man in 1991.

The cave was later made public in 2009 by a group of British scientists from the British Cave Research Association after they extensively surveyed the area.

Son Doong has a length of at least 6.5 kilometres and is estimated to be 200 metres in width and at least 150 metres in height (its largest chamber reaches an incredible 250 metres in height, enough space to accommodate 40-storey skyscrapers).

It contains at least 150 individual grottos, a dense subterranean jungle, and several underground rivers.

US photographer Ryan Deboodt said millions of US viewers had an opportunity to admire the floral system, untouched tropical forests and wondrous rivers and sands inside the cave, creating a one-of-a-kind natural wonder.

He said it is hard to demonstrate the cave’s incomparable beauty in words.

Programme host Ginger Rene described the caves as never-before-seen and breathtakingly beautiful destinations in the world.

Son Doong is expected to be the most outstanding symbol of Vietnam’s tourism in the future.