Spain ? A group of 30 scientists and nature lovers got lost in a maze of narrow underground tunnels in Spain’s Canary Islands, and six of them died after apparently suffocating, officials said Sunday.

The explorers were more than a mile underground Saturday in area where gases may have seeped in, cutting off their oxygen, said Jose Andres Garcia, emergency services director.

Eustaquio Villalba, a spokesman for the Tenerife Friends of Nature Association, said the six likely died when they inhaled air filled with carbon dioxide.

“It doesn’t smell bad or of gas and causes a depletion of what little oxygen is available down there, given there is no ventilation,” he said.

One person who managed to make it out alerted emergency services. But it took 17 hours for the bodies of five men and a woman to be pulled from the underground complex, known as Piedra de los Cochinos. Six others were flown to a hospital.