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.

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.