Thai officials had said Sunday that they were temporarily suspending the rescue effort so they could replenish oxygen supplies and other gear.
A helicopter with the boy on board was seen taking off shortly afterwards to the cheers of the crowd below.
Authorities have been tightlipped about the progress of Monday's operation.
"This morning they said they were hungry and wanted to eat khao pad grapao", Narongsak said referring to a Thai dish of meat fried with chilli and basil and served over rice. Four more boys and their coach still remain inside the cave. He said the next phase of the operation would start in 10-20 hours.
Four ambulances were seen leaving the Thai cave site Monday.
It was not clear who was inside the ambulance or the helicopter.
The second day of the underground rescue attempt began at 11:00am local time (2:00pm AEST). That left four boys and the team's coach trapped inside as the operation was called off for the day.
It is unclear which boys have been pulled out and which still remain in the cave.
Officials later confirmed the operation was under way again from about 11am local time (5am BST). "We can't visit our boys in hospital because they need to be monitored for 48 hours", Somboon told Reuters.
Eight boys are still inside the cave and along with the team coach.More news: Donald Trump defends USA position against global breastfeeding resolution
Finally, the 13 were discovered deep inside the mountain, fleeing rising waters and depleting oxygen levels.
There was no immediate word on their conditions. Previously, the entire round trip through the cave network was thought to take about 11 hours. Each of the rescued boys has been guided through the dark winding cave by a pair of divers.
He later visited the eight rescued boys at the Chiangrai Prachanukroh Hospital.
Weather forecasters warned heavy rain could hit the area on Monday afternoon and continue through the week.
The rescued boys were being treated by medics at the field hospital, and were later airlifted to a larger nearby hospital.
The four boys rescued from the cave on Sunday night have been declared in "good overall health" though they are waiting for the results of tests. "Testing for 3 more hours in LA, then it's on a plane to Thailand", Musk tweeted.
Rescuers sought to take out the boys in the weakest condition first. Four came out Monday, and it is possible Tuesday's plan was to bring out four more.
The most risky part of the journey out of the labyrinth cave system is the first kilometer, during which they are required to squeeze through a narrow flooded channel.
Dozens of divers have arrived at the cave on Sunday morning. They were quickly transported to a hospital in the town of Chiang Rai, the provincial capital.
The rescued kids are now in the hospital, where they should receive the proper care before being released to their families.
Night's relatives have said they believe the group went to the cave to celebrate his 16th birthday after a Saturday football practice and got caught as heavy rains caused the water inside the cave to suddenly rise.