At least 13 workers have been killed and another seven injured in a landslide at an unlicensed mine in southern Colombia, local officials say.

Witnesses described hearing an explosion at the open-air artisanal gold mine on Wednesday afternoon, moments before the workers below were trapped.

Emergency workers and locals were able to retrieve the bodies with the help of diggers.

Deadly accidents are not uncommon in Colombia, especially at unlicensed mines where locals dig for precious metals without any official oversight.

Witnesses said that four of the 13 dead were members of the same indigenous family.

Residents of the area said some 50 people, most of them members of the Quillacinga indigenous group, regularly worked in the mine near Policarpa, in southern Nariño province.

Between 200,000 and 400,000 people are estimated to engage in artisanal mining in Colombia, with many families relying on the income from selling the precious metals and stones they find to make ends meet.