The emerald, weighing 536 kilograms and measuring 125 centimeters in length, 78cm in depth and 55cm in height, has been on display at the BaoQu Tang Modern Art Gallery in Tsim Sha Tsui since June 20.

It has been named Gift from Heaven by Chinese painter Chan Sicpo, a longtime Madagascar resident whose works are also on display in the gallery.

Officials from the Madagascar judiciary, police and procurator's officer have arrived in Hong Kong, claiming the gem was declared as "green jade" when it was illegally exported. It was allegedly shipped out of Madagascar through the French colony of Reunion Island.

A spokesman of the gallery said the emerald belonged to a French company, Orgaco, which won a legal battle with the Madagascar government over the ownership of the emerald while it was in Reunion.

However, the ruling by a Reunion court may not be legally binding in Hong Kong, according to Hong Kong University Faculty of Law assistant professor Eric Cheung Tat- ming. Cheung added the Madagascar government can only stop the emerald from being exhibited through civil procedures.

According to the gallery, the emerald was extracted from an open-cast mine at Morafeno, a small town located in the southeastern region of Madagascar, in July last year. It was extracted using traditional mining methods that normally break the emeralds. However, this gemstone remained intact.

Madagascar is an island nation in the Indian Ocean off the southeastern coast of Africa and is the world's fourth-largest island. It is one of the world's major suppliers of gemstones.