HANOI - UNESCO will deploy a team of experts to assess possible risks for the conservation of Ha Long Bay in Vietnam as it is worried about development projects that may threaten the heritage-listed tourist attraction, the U.N. agency told Reuters.

The bay and the adjoining Cat Ba archipelago of limestone islets celebrates this year the 30th anniversary of inscription on the UNESCO world heritage list, being considered by the agency "the most extensive and best known example of marine-invaded tower karst."

The UNESCO designation contributed to the site becoming a massive tourist destination, drawing millions of visitors every year and boosting Vietnam's revenue from tourism.

However, the United Nations' education, scientific and cultural agency, in a statement attributed to its World Heritage Centre, said there were long-standing concerns that "multiple development projects for new tourism and urban residential areas along the coastline in Ha Long City had been approved and implemented" without a proper assessment of their impact.

The assessment mission, if it led to sanctions or even removal from the heritage list, could have a significant impact on Vietnam’s tourism sector, which accounted for eight percent of GDP last year according to official estimates.

"If threats are identified which jeopardize the integrity of the property and the reasons for which it was inscribed on the World Heritage List, the Committee may request corrective measures to strengthen the protection of the site," UNESCO said.

The mission, which will include experts from UNESCO and the International Union for Conservation of Nature, will be deployed in the coming months, UNESCO said.

Nuno Ribeiro, senior lecturer on tourism at RMIT University Vietnam, said overbuilding "threatens the bay's unique natural beauty, biodiversity, and ecological balance, which are the very attributes that earned it the UNESCO listing".

"The threat of corrective measures should not be taken lightly," he added.

Vietnam's culture and foreign ministries did not immediately reply to requests for comment, nor did the provincial authority responsible for Ha Long Bay.