The Semipalatinsk nuclear facility in Kazakhstan -- once the world's biggest nuclear testing ground -- has finally been closed.

One-hundred tons of conventional explosives were used in a huge underground blast to seal the last tunnel at the site.

Nearly five-hundred nuclear bombs were detonated at Semipalatinsk during its time as a testing centre, and the Kazakh government estimates that more than a million people were exposed to radiation as a result.

The BBC Central Asia correspondent says Semipalatinsk was so secret during the Soviet era that it didn't appear on the map and even the local population -- many of whom suffered from birth defects or cancer as a result of the tests -- didn't know what was taking place there.

From the newsroom of the BBC World Service