An explosion and a fire at a coal mine in western Turkey killed at least 70 workers on Tuesday and trapped another 200 or more miners underground, the country’s disaster agency said as it launched a massive rescue operation.

A power distribution unit exploded at a mine in the town of Soma, local official Mehmet Bahattin Atci told reporters.

Turkey’s disaster and emergency management agency, which gave the death toll, said about 20 people had been evacuated from the site so far, 11 of them with injuries.

The accident occurred during a shift change so the exact number of trapped workers trapped was not known. Mr. Atci had said the blast trapped between 200 to 300 miners but the disaster agency later gave the number as “more than 200 workers.”

“Evacuation efforts are underway. I hope that we are able to rescue them,” Prime Minister Recep Tayyip Erdogan said in televised comments.

Rescuers were pumping fresh air into the mine and rescue teams from neighbouring regions rushed to the area, said Energy Minister Taner Yildiz, who went immediately to Soma to oversee the rescue operation.

“It is a serious accident,” he told reporters. “Our priority is to reach our miner brothers.”

The rescue effort was being hampered by the fact that the mine was made up of tunnels that were kilometres long, said Cengiz Ergun, the leader of Manisa province, where the town is located.

SOMA Komur Isletmeleri A.S., which owns the mine, confirmed that a number of its workers were killed but would not give a specific figure. It said the accident occurred despite the “highest safety measures and constant controls” and added that an investigation was being launched.

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