The official declined to be identified as he is not authorised to speak to the media.
The boys and their coach went exploring in the massive Tham Luang Nang Non cave on June 23 after a soccer practice, and were cut off when a rainstorm flooded the cave.
The unsafe bid to rescue the boys - aged between 11 and 16 - resumed after a break on Sunday night to replenish oxygen supplies and make other preparations deep inside the cave complex in northern Thailand's Chiang Rai province. Thai Navy SEALs and global cave diving experts brought out four boys Sunday, and the operation is continuing today. There was heavy rain reported in the area, but that did not change the level of the water in the already flooded cave.
Getting all of them out the same way they came in was always a long shot, but so far one proving itself with two days of good news.
The Facebook page of the Thai Navy SEALs, who have been central to the rescue operation, was updated Monday night to say "two days, eight boars" - a reference to the Wild Boars, the name of the boys' soccer team.
A total of eight boys were removed from the cave on Sunday and Monday.
He told reporters the four rescued boys were taken to the hospital in the town of Chiang Rai, the provincial capital, for evaluation, and the next phase of the operation will resume after about 10-20 hours.
There was no word on the condition of any of the people brought out on Monday.
None of them have fevers, and all are able to eat normal "medical" food, the doctor said, an improvement from the watered-down porridge they were fed when they were first rescued.
Among those are United States military partners, British cave diving experts - including the two men who first located the boys a week ago - and rescue workers from Australia, China and other countries.
The world has been hooked on the fate of the group of Thai boys trapped in a cave and the heroic attempts to rescue them.
The hint of setting sun and blue skies broke through the heavy clouds behind the caves as a helicopter whirred through the sky, carrying the last of the team south to a hospital in nearby Chiang Rai.
Medical teams previously said concerns included hypothermia and an airborne lung infection known as "cave disease", which is caused by bat and bird droppings.
"I feel very happy, everybody is happy", said Hnin Jaiwong, the mother of one of the trapped boys, 13-year-old Sompong Jaiwong.
'We have not been told which child has been brought out.
The families of Thai boys rescued after a harrowing two weeks trapped in a cave deep underground will be allowed to see them today, but will be told not to hug or kiss them until health checks are complete.
At least nine ambulances loaded with stretchers and blue oxygen tanks waited by the mouth of the cave on Monday. Soldiers, medics, engineers and volunteers in yellow shirts milled around but the mood was relaxed.
One particularly touching note from another boy said: "I'm doing fine, but the air is a little cold, but don't worry. And we have more expertise than yesterday", he said.
The only way to bring the boys and their coach out of the cave is by navigating dark and tight passageways filled with muddy water and strong currents, as well as oxygen-depleted air.