Hạ Long Bay has an area of around 1,553 km2, including 1,960–2,000 islets, most of which are limestone. The core of the bay has an area of 334 Sq km with a high density of 775 islets. The limestone in this bay has gone through 500 million years of formation in different conditions and environments. The evolution of the karst in this bay has taken 20 million years under the impact of the tropical wet climate. The geo-diversity of the environment in the area has created, including a tropical, oceanic and sea shore bio system. Hạ Long Bay is home to 14 endemic floral species and 60 endemic faunal species.

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