A 3.4 magnitude earthquake in southern Poland jolted a coal mine Saturday morning, initially trapping seven miners more than half a mile (almost 1 kilometer) beneath the surface.

Eight teams of rescuers were at the Jastrzebie Coal Company site near the Czech border, trying to locate the missing miners.

Latest developments

The quake hit the Zofiowka coal mine at about 11 a.m. (0900GMT/UTC) in the southern town of Jastrzebie-Zdroj.

The rescue effort was launched at 11:25 a.m. For several hours rescuers were hampered by high levels of methane.

By late afternoon two of the seven trapped miners were rescued, hurt but conscious.

Rescuers were preparing a new corridor for extraction.

Family members of the missing miners are at the site, and psychologists are on hand to help them.

The main office building of the Zofiowka coal mine

'Powerful tremor'

Katarzyna Jablonska-Bajer, a spokeswoman for the coal company, said the blast was unusually strong. "There has never been such a powerful tremor at the mine."

Coal in Poland: Coal mining remains a major industry in a country still heavily dependent on the dirty fuel source for electricity and heating. But Poland is beginning to move towards cleaner renewable energy sources.

Coal in decline: The government's statistical office reports that 58.7 million tons of coal were extracted in 2017 — a decline of 4.8 million tons from the previous year.

Safety improving: A 2016 report by Poland's State Mining Authority, in the southwestern city of Katowice, concluded that mine safety in the country was improving. The report said the 2,074 mining accidents in 2016 represented a 26-percent decline over 2012. But the number of fatal accidents (27) in 2016 was virtually unchanged from four years earlier.

bik/aw (AP, Reuters, AFP)

Read more: Four killed in Polish mine after earthquake hits (2016)