Miners began a work stoppage on Tuesday to mourn the victims of Spain’s worst mining accident in 18 years, a gas leak that killed six people.

A 38-year-old Spanish miner was in serious condition after Monday’s accident at a north-western coal mine and four others were reported to be recovering from their injuries, local officials said.

The accident occurred as 11 men were working at a depth of 694 metres in the municipality of Pola de Gordon. Survivors said the miners accidentally breached a pocket of lethal methane gas that had accumulated in the mine.

More than 800 miners planned to stop work for 48 hours to mourn their colleagues in the region of Castile and Leon, which decreed three days of mourning. The six dead were to be given a collective funeral on Wednesday.

The company running the mine was investigating the accident.

Spain’s mining industry has been in decline for two decades as the country relies on new energy sources. Spanish coal mines employ about 5,000 people, down from more than 50,000 people in 1981.

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