The caves are between 400m to 4km long and range from 60m to 100m wide. All of them remain intact and have a startling display of beautiful stalactites.

The Phong Nha-Ke Bang National Park is working with the cavers to establish their exact dimensions and condition so they can decide on the best ways of protecting them while at the same time developing the local tourist industry.

Phong Nha-Ke Bang is a national park in the centre of Quang Binh province in north-central Vietnam . It protects one of the world’s two largest karst regions with several hundred caves and grottos.

It was first recognised as a world natural heritage site by UNESCO in 2003.

(Source: VNA)