MAE SAI, Thailand (AP) — Authorities overseeing the rescue operation for 12 boys and their soccer coach from a flooded cave in northern Thailand said they have a “limited amount of time” to get them out, as they raced against worsening weather and lessening oxygen underground.

The massive operation inside and around Tham Luang Nang Non cave suffered its first death Friday when a former Thai navy SEAL passed out underwater and could not be revived.

“We can no longer wait for all conditions (to be ready) because circumstances are pressuring us,” Thai SEAL commander Arpakorn Yookongkaew told a news conference. “We originally thought the boys can stay safe inside the cave for quite some time, but circumstances have changed. We have limited amount of time.”

Oxygen levels are decreasing because of the amount of workers inside the cave and workers were trying to run an oxygen line into the chambers in addition to the oxygen canisters used by divers, Chiang Rai province Gov. Narongsak Osatanakorn said late Thursday.

A senior army commander, Maj. Gen. Chalongchai Chaiyakam, said the most pressing mission is the oxygen line. It is tied to a telephone line to provide a channel of communication for the kids, who are stuck deep in the complex but are being looked after by four SEALs, including a medic.