Warsaw — Two missing coal miners were found hurt but conscious after a tremor struck a mine Saturday in southern Poland, and rescue crews were still trying to reach five other missing miners, a Polish mining company said.The rescue operation was launched at 11:25 on Saturday after a tremor occurred at the Zofiowka coal mine, said Katarzyna Jablonska-Bajer of the Jastrzebie Coal Company. The mine is located in the southern town of Jastrzebie-Zdroj near Poland's border with the Czech Republic.She said four miners were brought to the surface but contact was lost with seven others who were 900 metres underground, preparing a new corridor for extraction work.At first, high methane levels in the mine prevented rescuers from trying to reach the site but after four hours they began to head there. After the two miners were brought to the surface, ambulances took the injured men to the hospital.Miners' relatives gathered in front of the mine Saturday waiting for latest information, while the families of the missing were brought into the building and were being informed by mine management about the rescue efforts.Prime Minister Mateusz Morawiecki was traveling to the mine.Poland's State Mining Authority said the tremor had a magnitude of 3.4 on the Richter scale, while the European Mediterranean Seismological Centre pegged it at 4.3 magnitude. TVN24 said the tremor was also felt on the surface and shook some houses."There has never been such a powerful tremor at the mine," Jablonska-Bajer said.Coal mining is a major industry in Poland and coal remains the main source of energy and heating, but Poland is taking some steps to shift toward renewable, cleaner sources of energy.The Main Statistical Office says some 65.8 million metric tons of coal were extracted last year in Poland, some 4.8 million tons less than in 2016.Many of Poland's mines are dangerous, with methane gas in them that has led to a number of deadly explosions and cave-ins.So far this year, four miners have been killed in accidents in different coal mines in Poland, according to the State Mining Authority.