Fresh controversy has broken out after authorities in central Quang Binh Province last week allowed a survey project to set up a cable car system connecting many of the caves – and even enter the world's biggest, Son Doong.

Untouched: Son Doong Cave in Quang Binh Province. — Photo courtesy of Ryan Deboodt

The system will include 10.6km of cable running from Tien Son cave to Phong Nha, Thien Duong and Son Doong caves and ending at Tra Ang stream.

The system will eventually have seven cable stations, including three at Son Doong, which is more than 200m wide, 150m high and about 9km long.

It is still said to have "fantastic nature" inside. Adventurous trekking tours to Son Doong are limited and expensive. This year, about 240 visitors paid several thousand dollars each to join the first tours.

Many people are saying that the cable car actually entering the cave will negatively affect the cave, destroying its appeal for most foreigners.

Howard Limbert, a member of British Cave Research Association group that explored inside Son Doong in 2009, was quoted by Tuoi Tre (Youth) newspaper as saying that mass tourism would destroy the beauty of the cave and cut the feeling of adventure.

He warned that while mass tourism would bring many benefits, the losses would be huge. He warned that foreign tourists who loved adventure would turn their backs on Son Doong.

Many other people oppose the cable project and their opposition has created an outcry in the local media.

Nguyen Huu Hoai, chairman of Quang Binh Province People's Committee, said that the present work was "a surveying project and the decision to develop a cable-car system had still to be decided".

However, he promised to give conservation of Son Doong "top priority".

Meanwhile, Le Thanh Tinh, director of the Phong Nha - Ke Bang National Park, which is a UNESCO world heritage site including the cave, said he supported the project.

Tinh said he had worked with the investor of the cable-car system and "found out that the system would not have negative environmental impacts".

Oxalis Adventure Tours, the exclusive operator of adventure tours to the cave, has announced that from January to August next year about 450 visitors will be allowed to trek inside the cave.

Nguyen Chau A, Oxalis director said that he "was in a position that he could not say anything against the cable system project" but promised efforts to conserve the cave as he could do.