Bogota: A massive uncut emerald on exhibit in Colombia's capital is being touted by its owners as the biggest in the world, officials said.

The 11,000-karat raw green gem weighs in at 2.27 kilos and is on show in Bogota 12 years after it was mined in Muzo, in the South American nation's emerald country in Boyaca province.

"It is priceless," Santiago Soto, spokesman for the Minergemas 2011 gem industry trade fair under way in Bogota, said of the stone owned by the firm Coexminas.

No more than 15 people at a time are allowed to view the stone, with five guards looking on.

Colombia produces 55 per cent of the world's emeralds, exporting them for about USD 200 million a year.