Rescuers have started to enter the cave, with a team of global diving experts attempting to free the 12 schoolboys and their 25-year-old coach.
An Australian doctor who is part of the global team of rescuers checked the health of the boys Saturday to decide who should be brought to the surface first.
According to BBC News, the team began the operation ahead of schedule thanks to a pause in the frequent rains that come with the country's monsoon season.
His death highlights the very grave danger caused by conditions in the cave, where the situation can quickly worsen due to flooding.
At 10am local time, 18 divers went into the cave to bring out the boys - including 13 global divers and five Thai Navy Seals.
"His buddy tried to give him first aid, but he did not respond".
"We are giving them a physical examination". It was not immediately known if a US diver was among them. Each of the rescued boys had two divers with them at all times during the operation.
The rescue mission began after rain showers soaked the Tham Luang Cave area in northern Chiang Rai province for the past 24 hours, heightening the risks in what the governor has called a "war with water and time" to save the team.More news: Julius Randle reportedly signs two-year, $18 million deal with Pelicans
Local officials said there is a small window of favorable conditions to start the rescue mission.
The boys, ages 11-16, and their 25-year-old coach became stranded when they went exploring in the cave after a practice game.
Half of the soccer team trapped inside the flooded Thai cave have now been brought out after divers executed a carefully constructed rescue mission.
Rescuers have suggested that it may take up to two days for the rescue to be completed, with each boy being brought out individually.
Image: Rescuers searching for 12 missing boys and their football coach say they have all been found alive, officials in Thailand have said.
Thai rescuers are being assisted by an worldwide team comprising experts from China, Australia, the USA and Britain.
The Thai boys trapped in a cave for two weeks have written letters to their parents, saying "don't worry. we are all strong".