A team of seven Japanese film makers, together with three cave explorers from the British Cave Research Association, on May 9 started work on a 3D documentary on the world's largest cave in Phong Nha-Ke Bang National Park in the central province of Quang Binh.

According to Luu Minh Thanh, director of the park's managing board, the documentary will offer researchers a better chance at understanding the origins of the cave, known locally as Son Doong, the forests and the fast flowing underground river inside. Thanh added that the film would be broadcast in 160 countries and territories across the globe.

The cave, feared by locals for the whistling sound its underground river makes, was first discovered by a local man named Ho Khanh in 1991. It was only in 2009, when a group of British scientists from the British Cave Research Association, led by Howard Limbert, conducted a survey in Phong Nha-Ke Bang on April 10-14, that the existence of the cave was made known publically however.

According to Limbert, the cave is five times larger than the nearby Phong Nha cave, previously considered to be the largest cave in Vietnam . The largest chamber in Son Doong is over 5km in length, 200m in height and 150m in width.

Phong Nha-Ke Bang National Park was first recognised as a world natural heritage site by UNESCO in 2003 for its geological value. Pending a decision in July this year, the United Nations cultural body plans to further honour the park a second time round for its biodiversity./.