Five others were taken to hospital in Leon in northwestern Spain after the gas leak at the Santa Lucia mine, the spokesman said.
Emergency services had initially reported that five people had died.
"There seems to have been a leak of methane gas," Francisco Castanon, the mayor of the municipality of Pola de Gordon where the mine is located, told local television.
Spain's coal mining sector has been contracting for decades, with a reduction in government mining subsidies hastening the closure of unprofitable mines.
Around 40 coalmines are still in operation, mainly in the north of the country, employing some 8,000 miners.
Like other European countries, Spain has committed to gradually close unprofitable coalmines in the next few years.
More details to follow.