Three workers who were trapped by a controlled detonation and gas leak at a potassium mine in Germany died Oct. 1, an official said.

The Associated Press reported that rescue workers found the bodies of the three men while searching the depths of the mine in Unterbreizbach in the eastern state of Thuringia, said a spokesman for K + S GmbH, the company that owns the mine, The Associated Press reported. 

“Three miners aged 24, 50 and 56 were killed during the detonation that led to an outbreak of carbon dioxide,” said Ulrich Goebel said. “The company is deeply shocked.”

Initially, seven miners were trapped about 700 m (2,300 ft) below ground, but four of them were quickly rescued, two of them requiring medical treatment, the Kassel-based company said on its website.

Two mines and their shaft installations above ground were evacuated when the accident occurred around noon Oct. 1, leading to a large release of dust inside the mine where the detonation took place, trapping the miners.