There has been a rush for tickets to explore Son Doong Cave, the largest in the world, next year.
Chua Me Dat (Oxalis) Adventure Tours, the exclusive tour organizer, said Quang Binh Province authorities have decided to allow only 640 visitors next year.
“Depending on weather conditions, Oxalis may organize tours for 500-600 tourists,” the company said in a statement August 15 when it opened the sale of tickets.
Thousands of people have sought tickets, which would be sold on and a first come, first served basis to those who satisfy health requirements, the company said.
Oxalis has been organizing five-day tours to the cave with 10 people at most.
The cave opens from January to August every year to avoid bad weather.
This year 442 people have visited so far, including a group of diplomats from several countries like Argentina, Sweden, Italy, and the Czech Republic.
Oxalis, headquartered in the Phong Nha Ke Bang National Park in Quang Binh, has been organizing tours to Son Dong Cave since 2013.
A tour party usually comprises around 25 people, including porters, a cook, a tour guide, two cave experts and two park rangers.
Tickets for 2017 cost VND66 million (US$3,000) per person.
Tourists are required to be fit enough since the tour involves a trek of 50 km (31 miles) in a jungle and mountain; elevation of up to 400m (between road and valleys); 40 river crossings (10-50m wide river, knee deep); 10 km caving including rope climbing, rocky terrain and scrambling; 80m descent with rope and harness; crossing underground rivers with strong currents and five days inside.
Son Doong, which is 150 meters high and 200 meters wide, became known worldwide in 2009 when it was explored by members of the British Cave Research Association together with local man Ho Khanh.
Oxalis often sells out its tours well before it starts.
In July the company obtained a license to organize tours to the Tien 2 Cave, which discovered earlier this year.