efe-epaLa Paz

Eight people were killed and twelve others injured by an explosion on Wednesday in a mine in Bolivia, a tragic incident that led the labor unions to declare a one-month national mourning and prompted the Bolivian president to launch an immediate investigation into its causes.

The explosion occurred in Huanuni, in the west of the country, at 03:45 local time (07:45 GMT), when the third of four trucks that were entering the mine with workers on board exploded, Bolivia's Minister of Interior Carlos Romero told state radio station Patria Nueva.

The injured were taken to the Huanuni health center and other hospitals in the nearby city of Oruro, where some still remain in critical or serious condition, according to medical reports.

Most of the injured suffered multiple contusions and fractures. Several of them needed to undergo surgery while one had to have his leg amputated.

The Bolivian Workers' Center (COB) declared thirty days of national mourning along with other labor unions, and asked the Government to deploy military and police personnel at the mine, fearing that a similar tragedy could happen again.

In a statement to local media, COB chief Juan Carlos Huarachi pointed to the so-called "jukus" mine thieves as the ones responsible for the incident but the authorities have yet to determine the cause.

Bolivian President Evo Morales ordered the ministries of interior and justice to conduct an immediate investigation into the explosion, while expressing his solidarity to the families of the casualties, the COB and the Union Federation of Bolivian Mine Workers (FSMTB).

The commander of the Bolivian Police, Faustino Mendoza, told local media that "multidisciplinary team" is collecting evidence at the scene.

Oruro's Prosecutor Mario Rocha said that the bodies of the deceased will be kept at the Huanuni stadium until the funeral on Friday.

Mines in Bolivia are often the scene of toxic gas inhalation, landslides and, to a lesser extent, explosions.