At least 13 miners have been trapped in a collapsed gold mine in far eastern Russia, regional officials said Tuesday.

Part of the mine collapsed in Zeysk district, authorities in the Amur region said.

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The Emergencies Ministry reported that 13 miners were trapped, but the regional prosecutor’s office said that up to 15 could remain underground.

A rescue operation has been launched.

Emergency responders were trying to reach the miners, who were trapped at a depth of 125 meters (410 feet), via a ventilation shaft, Russian media reported.

Officials didn’t immediately say what caused the accident. Most mining accidents in the past have been blamed on violations of safety rules.