The second phase of a rescue operation has ended for the day, with more than half of the Thai soccer team rescued from the cave.
Authorities have said extracting the entire team from the cave could take up to four days, but Sunday's success raised hopes that it could be done faster.
But he could not confirm if all five would come out today. He said the metal tube of the device is "light enough to be carried by 2 divers, small enough to get through narrow gaps" in the cave system.
Elon Musk's Space X rocket company is testing a "kid-sized submarine" that could be sent to help boys trapped in a flooded Thailand cave.
Rescuers had spent days balancing the risk of impending monsoons, which could have flooded the cave again, against the boys' readiness, weakened as they were by their ordeal.
A device by Elon Musk's SpaceX and The Boring Company, created to help rescue the remaining members of a soccer team trapped in a flooded cave in Chiang Rai, Thailand, is being tested in a swimming pool in Los Angeles, California, in this still image taken from an undated video obtained from social media.
The story of the boys and their novice monk-turned-soccer coach from this small town on the Thai-Myanmar border - remarkably found alive nine days after they went missing June 23 - launched an worldwide rescue effort and intricate planning on how to maneuver all 13 safely through the narrow passageways and ink-black waters.
Each boy is being accompanied by two divers and it takes several hours to negotiate the flooded tunnels through the dark, murky water.
A Reuters witness near the Tham Luang cave in the northern province of Chiang Rai saw medical personnel carrying two people out of the cave to waiting ambulances on Monday evening.
He did not say how many boys the team hoped to bring out on Monday.
The saga has dominated global headlines, with the team spending nine days unaccounted for inside the cave before British divers found the emaciated and dishevelled group huddling on a muddy bank.
"All 12 wild boars and the coach have left the cave. all safe".
Monsoon flooding cut off their escape route and prevented rescuers from finding them for nearly 10 days.
Describing Monday's rescue, the first source said the boys arrived at Chamber 3 at 4pm after being rescued by foreign and Navy Seal divers from the ledge called Nern Nom Sao, where they had sheltered from floodwaters for more than a week.
Preparations are also under way to manage the mental health of the boys once they are all freed.
Thailand officials have not released the names of the boys rescued, so as not to upset the parents of any child still trapped. A former Thai navy SEAL passed out and died making the dive Friday.
Four others were extracted Sunday.
Giving an update on the four boys pulled from the cave Sunday, Narongsak said, "This morning, they said they were hungry and wanted to eat khao pad grapao" - a popular Thai rice dish of meat stir-fried with basil and chili peppers.
"No hugging" or "touching" would be allowed between the boys and their relatives, however, until all medical tests are completed, the official said.
The rescue mission is expected to resume Tuesday morning local time to bring out the remainder of the team.
The fate of the boys and their coach has gripped Thailand and drawn worldwide media attention. "We are giving them a physical examination". Two of them possibly have a lung infection but all eight are generally "healthy and smiling", he said. More than 1000 journalists from across the world have descended on northern Thailand to report the story. He said rescuers told the parents that the "strongest children" would be brought out first.
"We have not been told which child has been brought out". We've got good news for you. One was that it was unknown how safe and dry the area where they had taken shelter would stay as Thailand's rainy season, which lasts until at least late October, picks up pace.
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