Halong Bay is made up of 1,969 islands of various sizes, 989 of which have been given names. There are two kinds of islands, limestone and schist, which are concentrated in two main zones

The islands in Ha Long Bay are mainly limestone and schist islands most lying in the two main areas: the southeastern part of Bai Tu Long Bay and southwestern part of Ha Long Bay. These islands represent the most ancient images of a geographical site having a tectonic age of from 250 million to 280 million years. They are the result of many times of rising and lowering processes of the continent to form a karst. The process of nearly full erosion and weathering of the karst created the unique Ha Long Bay in the world. In a not very large area, thousands of islands with different forms look like glittering emeralds attached to the blue scarf of a virgin. The area where many stone islands concentrate has spectacular scenes and world-famous caves and is the center of Ha Long Bay Natural Heritage, including Ha Long Bay and a part of Bai Tu Long Bay.

The area is recognized as the World Natural Heritage that is the area of 434 sq. km with 775 islands. It looks like a giant triangle with Dau Go Island (in the west), Ba Ham Lake (in the south) and Cong Tay Island (in the east) as its three angle points. The nearby area is the buffer area and areas classified as national beauty spots in 1962 by the Ministry of Culture and Information.

Viewed from above, Ha Long Bay looks like an extremely vivid huge drawing. This is a wonderful and skilful masterpiece of the Creation and of nature that turns thousands of dumb soulless stone islands into fantastic sculptural and artistic works of various graceful shapes, both familiar and strange to human beings.