Twelve boys - aged between 11 and 16 - and their coach, were discovered by two British divers on July 2, nine days after they disappeared during an outing in the Tham Luang Nang Non cave complex, in Chiang Rai, northern Thailand. But, their conditions are unknown.
"They are now at the field hospital near the cave", Tossathep Boonthong, chief of the health department in Chiang Rai in northern Thailand, told Reuters earlier.
Mr Narongsak said that the rescue operation could take a number of days or be halted at any time. Although, dozens more divers are on hand to assist.
The boys urged relatives "not to worry" and asked for their favourite food once they were safely evacuated, in notes handed to divers.
After an initial assessment at the site, the boys were airlifted to a makeshift helipad close to the Chiang Rai Prachanukroh hospital, some 70km away.
The effort's leader, Chiang Rai acting Gov. Narongsak Osottanakorn, said the earliest that the first group of boys was expected to emerge is 9 p.m. local time - about 11 hours after the start of the operation. They will be accompanied by an "all-star" team of 13 worldwide and five Thai divers, officials said.
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Now that the first of the boys have been taken to a nearby hospital, doctors there will begin evaluating the impact to their long-term health.
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Narongsak said Sunday morning two divers would escort each of the boys out of the cave.
"There is no other day that we are more ready than today", he said. Rescuers have been unable to extend a hose pumping oxygen all the way to where the boys are, but have brought them some oxygen tanks.
Narongsak said that rescuers have assessed the boys' condition and also briefed their families, who are supportive of the rescue plan.
"Now and in the next three or four days, the conditions are ideal [for evacuation] in terms of the water, the weather and the boys' health", Narongsak in a press conference on Sunday. If something changes we'll stop.
In any case, it's instructive to see how the crowdsourced engineering exercise unfolded over the course of just a couple of days.
Dark clouds and fog shrouded the area around the cave as a steady rain began falling in the early afternoon.
Thailand's Meteorological Department said there was a 60 percent chance of rain Monday with thunderstorms forecast throughout the week.
"Don't be anxious, I miss everyone". I'm happy being here inside, the navy SEALS have taken good care.
"We are talking about it all the time", said Napattra Chokumpompan, 21, who works at a hotel in Mae Si.