Thanks to discoveries made during a recent expedition in Vietnam, it appears the world's largest cave, Son Doong, is even bigger than previously thought, US Cable News Network (CNN) has said.

CNN said last month, a trio of British divers ventured to Phong Nha-Ke Bang National Park to explore the cave's waterways.

During the groundbreaking dive, they discovered a new underwater tunnel that connects Son Doong with another enormous cave called Hang Thung.

Son Doong currently measures a total of 38.5 million cubic meters. When it's officially connected with Thung Cave, it will add an additional 1.6 million cubic meters in volume.

The divers plan to return in April again next year. This is the best time of year to dive, because water levels are relatively low, and visibility is better than usual -- though still only about one to two meters.

One of the world's most precious natural wonders, Son Doong was inadvertently discovered by Vietnam resident Ho Khanh in 1990.