WARSAW, Poland (AP) — Two methane explosions at a coal mine in southern Poland killed five people and injured more than 20 on Wednesday morning, Poland’s prime minister said. Seven other people were missing.

The first explosion took place shortly after midnight about 1,000 meters (3,000 feet) below the surface of the Pniowek mine in Pawlowice, Prime Minister Mateusz Morawiecki told reporters outside the mine’s office building.

Morawiecki said a rescue operation was launched immediately, but a second explosion occurred about three hours after the first and communication was lost with some of the rescuers.

The operation was suspended due to the resulting fire and unsafe conditions. Experts were evaluating the possibility of resuming the rescue mission.

The mine, near the Czech border, is operated by the mining company Jastrzebska Spolka Weglowa, or JSW. The prosecution has opened an investigation.

More than 20 people, including emergency workers, were hospitalized with serious burns, the prime minister said. Doctors at the Siemianowice Slaskie Hospital, which specializes in treating burn victims and mining accident victims, said some of the patients had life-threatening injuries, including burns to the lungs and large areas of the body.

Health Minister Adam Niedzielski said one of the 5 dead was among 11 injured who were taken to Siemianowice hospital in the most serious condition. Other injured people were transported to other hospitals in the region.

Rescue workers were among the victims of the explosions, Morawiecki said.

“A tragedy happened here today,” he said, offering sympathy to the families and highlighting the dangerous nature of the work in the coal mines.

Poland depends on its own coal and imported coal for almost 70% of its energy, drawing criticism from the European Union and environmental organizations concerned about CO2 emissions and climate change.

Most of the coal mines are located in the southern region of Silesia. Many are at risk of exploding from the sudden release of methane.

The government recently announced that it would end coal imports from Russia by May. The action is part of Poland’s drive to wean itself off dependence on Russian energy sources, but also comes in response to Moscow’s invasion of Ukraine.