Rescuers will enter a West Virginian coal mine in the US early Thursday US time to search for four miners missing since a fatal blast killed 25 workers two days ago.

Four rescue teams will head 8km into the Massey Energy mine to reach the refuge chamber, according to Reuters.

Before entering the mine, the team drilled holes deep into the Upper Big Branch mine to ventilate lethal carbon monoxide and highly explosive hydrogen and methane.

After testing the air quality at the bottom of a 1,100ft borehole, it was found that the amount of deadly gases had dropped to a safe level allowing rescuers to enter.