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.

Le Thanh Loi, director of the park’s tourism center, was quoted as saying that explorers found ancient limestone, stalactites and fossils possibly millions of years old.

The cave is as high as 80 meters with various terrains suitable for trekking, swimming and even climbing, according to Nguyen Van Tho, a member of the exploration team.

First discovered in 1990, Toi Cave had about 400 meters from its entrance opened to tourists nearly four years ago. It is currently part of a route connected with the Chay River and can be reached by a 400-meter zip-line from a wildlife observation deck.

In a service area nearby, tourists can explore with lights, swim in a pond where the water temperature is less than 20 degrees Celsius or take a mud bath.

Phong Nha-Ke Bang won UNESCO heritage recognition in 2003 thanks to its 300 different caves and grottos with unique limestone structures and the oldest karst formation in Asia, dating back some 400 million years.

But only some of the caves are accessible to the public, like the world’s largest cave Son Doong and Paradise, described as the world’s most beautiful cave and Asia’s longest dry cave by a British Cave Research Association team that explored it.

Official figures from the tourism center showed that more than 15,000 tourists visited the park during the Vietnamese New Year (Tet) holidays from February 19 to 23, up more than 10% from last year.

The center hopes to attract 490,000 visitors, including over 50,000 foreigners, to the park this year.