A spokeswoman says a methane gas explosion at a Polish coal mine has killed four miners and injured at least 19 others, AP reported. Borynia mine spokeswoman Agnieszka Warzycka says the blast occurred in a shaft about 2,950 feet (900 meters) underground near the town of Jastrzebie Zdroj. She said Thursday that five of the injured are in serious condition. The blast late Wednesday was Poland's most serious mining accident since a November 2006 methane gas explosion killed 23 miners in the Halemba mine.