The BBC's Helier Cheung has footage of an ambulance seen leaving the cave.
To get there, search and rescue teams including at least 90 divers have to pass through more than two-kilometers of narrow, flooded tunnels.
The ambulance drove toward a helipad, where a helicopter was seen taking off shortly after to the cheers of the crowd below.
A source inside the Chiang Rai Prachanukroh hospital where the boys are being kept said their condition was "not bad" but said doctors were watching for signs of emerging conditions such as hypothermia.
Now only five members of the team remain in the cavern complex, where they became trapped more than two weeks ago.
There are reports the divers re-entered the cave around 1pm local time Monday.
Engineers have been diverting the water flow into the cave over the past week and pumping it out at a rate of 180,000 litres an hour in an attempt to make it easier for the boys to escape and reduce the amount of time they must spend underwater.
Rescuers and the families of the 12 boys and their football coach being saved from a Thai cave complex are "cautiously optimistic".
Already the operation has killed one diver, former Thai navy SEAL, Saman Gunan.
His updates came after USA and Thai officials confirmed Sunday that four boys had been rescued from a flooded cave network after spending 15 days trapped along with their soccer team and coach.
Sunday, July 1: Divers inch further into the cave, as an operating base is set up inside and hundreds of air tanks and other supplies are pulleyed in.
Eight boys and the coach remain inside the Tham Luang Nang Non cave as authorities paused the global effort to replenish air tanks along the treacherous exit route. He said that process can take several hours.
Narongsak said the operation was going "better than expected".
But bringing out the remaining four boys and their coach could take more than one operation, Narongsak warned.
Bursts of heavy rain soaked the Tham Luang Cave area in Thailand's northern Chiang Rai province overnight, increasing the risks in what has been called a "war with water and time" to save the boys. But the Denver Fire Department captain said the rescue mission to save a youth soccer team in Thailand is "unbelievable". Operation chief Narongsak Osottanakorn said a total of 90 divers would be involved in the rescue mission, with 40 divers from Thailand, and 50 from overseas, including the United States, Australia, China, and Europe, according to the Washington Post.
Elon Musk, CEO SpaceX, have built a submarine to rescue the Thailand kids from the flooded Tham Luang cave.
Musk posted videos on Twitter of the aluminum sub being tested at a swimming pool at Palisades Charter High School today.
Interior Minister Anupong Paochinda told reporters that the boys rescued Sunday are in hospital and doing fine but require thorough medical checks.
Authorities temporarily stopped rescue efforts on Monday to replenish air tanks along the cave's perilous exit course. Before announcing that the rescue was underway, authorities ordered the throngs of media that have gathered at the cave from around the world to leave.
But Thai authorities had already began there rescue efforts before the vessel was completed without Mr Musk's help.
But in today's tweets, Musk made clear that he wouldn't consider the effort wasted even if it doesn't come into play in the flooded Thai cave.
"It is an extremely risky undertaking", Bill Whitehouse, vice-chairman of the British Cave Rescue Council, told AFP, adding "poor visibility in the water, tortuous passages to get through, constrictions" were some of the major obstacles divers face.
"Will continue testing in LA in case needed later or somewhere else in the future", he wrote.
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