Ukrainian officials say four coal miners have been seriously injured and at least 37 are missing after an explosion at a mine in the eastern Donetsk region. Maryna Nikitina, a spokeswoman for the industrial safety watchdog agency, says the explosion took place at the Karl Marx mine early Sunday about 1,000 meters underground. She says the four injured miners have been hospitalized with severe injuries, and at least 37 remain trapped in the mine. Ukraine has some of the world's most dangerous mines, due to outdated equipment and poor safety standards. Officials say that for every 1 million tons of coal brought to the surface in Ukraine, three miners lose their lives.