Authorities in Vietnam say they plan to ban fishing in the popular tourist area of Halong Bay, due to concerns about the fragile eco-system there. The move comes as worries are being expressed about the impact of over-tourism at the UNESCO heritage site. Tony Cheng has more.  

Jade green mountains serenely rising from calm emerald waters. This is Halong Bay in Vietnam. A site of such scenic beauty. It's become known as one of the most beautiful places in Asia. And recognized as a world heritage site by UNESCO. There is little serene or calm about Halong Bay today, however. Huge tour boats chug between the monolithic limestone mountains, carrying as many as fifteen thousand tourists a day. And at this time of year, around Mid-Autumn Festival and National Day, the stream of visitors has turned in to a flood.

TONY CHENG HALONG BAY, VIETNAM "This is one of the main sites on the Halong Bay tour, a stone formation known as the chicken. But around it are gathered all of these tourist boats. They're bumping and jostling and you can hear the chug of the engines. In the background you have the smokestacks of Halong city. It doesn't really feel like a place of exceptional national beauty."

At the ferry port, even more arrive to join the tours. The site is a huge draw for visitors from all over the world, and generates vital revenue for the local government. But success comes at a cost, and now anyone coming to Vietnam, HAS to visit.

STEVE AMERICAN TOURIST "I guess it's a must-see for any tourist coming here to Vietnam to see one of the natural world wonders."

TOURIST "Halong Bay, I call it the gem of the north because it's just so much different, it's beautiful, I love it."

Mass tourism has now turned the sleepy town of Halong into a rapidly growing city. Mountains have been carved out to make way for new apartments and hotels and building sites cram the shoreline for a view of the famous bay. Along the sand, the waste washes up, a reminder of the indelible mark the tourists leave behind.

DUONG BICH HANH CHIEF OF CULTURE UNIT, UNESCO BANGKOK "Respect the heritage and the local culture."

That is the message from UNESCO, guardians of world heritage sites around the world. They're now seeing a huge increase in mass tourism, particularly as China opens up. 

DUONG BICH HANH CHIEF OF CULTURE UNIT, UNESCO BANGKOK "Education is very very important, for people before they come, and for people during the time they come."

One of the options may be quotas to spread the numbers of visitors evenly throughout the year. Or raising ticket prices, to generate funds for conservation. And when you next go on vacation, try not to leave your mark. Tony Cheng, CGTN, Halong Bay Vietnam.