Scores of other volunteer cave divers from around the world helped by delivering air refill tanks and tightening the guide rope along the route, which includes ten "choke points" where the mud-clogged tunnel is terrifyingly narrow.
"The operation is being supervised by the Thai authorities".
Among the ideas were drilling an escape route through the mountain, or leaving them for months until the monsoon season ended and the flooding subsided.
Extracting everyone could take up to four days, but the initial success has raised hopes that could be done.
For the final operation tomorrow, Mr Narongsak said the rescuers would use the same plan with some adjustments because the number of survivors to be extracted would be five instead of four as was the case for the last two days.
Among these were that none of the boys had scuba diving experience, and that they could easily panic while swimming underwater in darkness.
The same divers who rescued the children on Sunday went back in to collect the next four on Monday, with the country's interior minister Anupong Paojinda saying they would conduct the next operation as they already knew of the cave's conditions and how to safely bring the children out.
The painstaking rescue has required breaks to allow the group of 18 elite divers to rest and replenish the cave with oxygen for the remaining soccer team members, ABC News reports.
The boys being rescued are not though.
The extreme danger of the rescue effort was underscored last week when a former Thai Navy SEAL, Samarn Poonan, died after he fell unconscious while placing oxygen tanks deep inside the cave. While no details were shared on their exact conditions, Dr. Jennifer Ashton, ABC News' chief medical correspondent, said doctors will likely evaluate their mental as well as physical condition.
Musk said the submarine, which is made from the liquid oxygen tube of SpaceX's Falcon rocket, is small enough to fit through the cave system's narrow passageways. If the tests were successful, the sub was to be placed on a 17-hour flight to Thailand.
Workers have been labouring around the clock to pump water out of the cave, and officials said that despite heavy downpours overnight, water levels inside the cave did not rise.
Musk posted videos on Twitter of the aluminum sub being tested at a swimming pool Sunday midafternoon California time.
President Donald Trump tweeted on Sunday: "The U.S.is working very closely with the Government of Thailand to help get all of the children out of the cave and to safety".
None of the boys' identities have been publicly revealed. "This morning they complained that they are hungry and they asked for fried basil with rice".
"Don't be anxious", wrote another boy, Mick. Please take good care of yourselves and cover yourself with blankets.
"The big worry that you get with caves is the presence of bats", said Dr. Amesh Adalja, a senior scholar at the John Hopkins Center for Health Security in Baltimore. "Although, don't forget to set up my birthday party".
"I beg Phra Pirun because the Meteorological Department said that from Monday on there will be continuous rain", Bancha said.