Colombian coal mine blast kills 21 workers

An explosion at a coal mine in north-eastern Colombia has killed 21, officials say.

The blast at the La Preciosa mine in Sardinata is thought to have been caused by a gas build-up.

In February 2007 a gas explosion at the same mine killed more than 30 workers.

The Colombian mining minister, Carlos Rodado, ordered the mine be closed indefinitely and said the supervision of mines across the country would be stepped up.

Emergency teams were at first unable to enter the mine because of a rock collapse and the danger of gas, officials said.

TV images showed anxious friends and relatives watching from the mine entrance hoping that their loved ones would be pulled out alive.

The BBC's Jeremy McDermott in Colombia said the small mine was rudimentary with only basic safety measures.

The blast happened early on Wednesday morning just as a change of shift was taking place.

Sardinata is in Colombia's Norte de Santander department near the border with Venezuela.

Last June an explosion at the San Fernando mine in Amaga, Antioquia province, north-west Colombia, killed 70 miners.

In November, nine workers died at two mines in the Cundinamarca region.

Colombia is one of the world's largest coal exporters and has the second-largest reserves in South America, after Brazil.

Although conditions for miners in South America have improved radically over recent decades, there are still many accidents.