Pressure is mounting on Thai authorities to bring forward a rescue plan for 12 boys and their coach trapped deep inside a flooded cave in northern Thailand, after the death of a former navy diver and a drop in oxygen levels underground.

Officials initially thought they could keep the boys and their coach in the cave where they are trapped for up to four months, until waters dropped sufficiently for them to be able to walk out. But the death of a rescue team member, and the realization that oxygen levels have fallen to potentially dangerous levels, appears to have forced a reassessment of the situation.

Thai Navy SEAL chief Rear Adm. Aphakorn Yoo-kongkaew said oxygen levels in the cave had dropped to 15 percent, a level that one Thai medic said posed a serious risk of hypoxia, the same condition that causes altitude sickness. It was too dangerous to leave the boys much longer, Yoo-kongkaew said, despite the risks involved in attempting to bring them out.

“We can no longer wait for all conditions (to be ready) because of the oppressive situation,” he told journalists Friday.

He did not say how long they could survive with current oxygen levels, but he said getting more oxygen to the boys was top priority.

Despite concerns, the boys are unlikely to be extracted within the next 24 hours because it was still too dangerous, according to a Thai Navy official.

One reason the team cannot yet be evacuated is that rescuers were also still searching for three more wetsuits with a thickness of five millimetres, the official told CNN. Three of the boys are too small for the wetsuits on hand.

But the number of rescue workers staying with the team in the chamber had been reduced from 10 people to five because of the lowered oxygen levels.

Authorities were pushing ahead with plans to free the team hours after former Sgt. Saman Kunan, a Thai ex-SEAL, died at 2 am Friday, as he returned from an operation to deliver oxygen tanks to the cave where the boys are located.

The 38-year-old ran out of air while underwater, an official said.

The boys, members of a youth football team, and their coach have been trapped in the labyrinthine cave at the Tham Luang Nang Non complex for nearly two weeks, unable to navigate their way out of a series of narrow passages after floodwaters forced them to take shelter on a rocky ledge.

The huge operation to rescue them involves dozens of Thai Navy divers, and experts and volunteer divers from parts of Europe and Asia, as well as Australia and the US. Billionaire inventor and entrepreneur Elon Musk said Friday engineers from his SpaceX & Boring Co. were heading to Thailand to see if they could help.

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