Thailand cave rescue: Former Navy SEAL dies in bid

A FORMER Thai navy SEAL who joined the rescue operation died on his way out from the cave complex after delivering oxygen tanks.

Thai authorities say the death was caused by a lack of oxygen inside the cave overnight, AP reports.

Rescuers continue to work day and night to save 12 Thai boys and their 25-year-old coach from the flooded cave before it's too late but some may be too weak to complete the terrifying mission.

Two of the boys and their football coach are suffering from exhaustion through malnutrition, which could make it almost impossible for them to attempt the perilous journey, a navy source told CNN.

It means rescuers could complete the mission in stages, with the boys who are well enough removed first and those that are too sick left behind.

The coach is believed to be in a bad way due to sacrificing his share of food to the boys, ABC reported.

A lack of oxygen and the approaching torrential rains also threaten to derail the risky plan to rescue the schoolboys.

They are trapped 3km into a system of linked chambers in Mae Sai, northern Thailand, as their frightened families wait at the cave entrance. It is believed they may have entered as part of an initiation rite, although two mothers came forward to say they did not blame coach Ekkapol Chantawong for their boys' desperate circumstances.

The 25-year-old coach and former monk is struggling after selflessly sacrificing his share of food, reported the ABC. But it is still possible he could be charged over the crisis.

First, the global rescue operation urgently needs to get the boys out.

Skilled cave divers are painstakingly teaching them to swim in preparation for a perilous escape, which involves pairing them with trained frogmen and leading them to safety through pitch-black water and narrow passageways.

Officials confirmed members of the team have started to learn to scuba dive, and some parts of the journey will be walkable.

It had been hoped the rescue would begin on Thursday, but the ambitious plan remains on hold as fears grow for the group.

Rescuers say they have to get the boys out within 48 hours before the rains hit.