At around 9.40pm AEST, the Thai Navy SEAL's Facebook page posted "12 wild pigs and coaches out of the cave. Safe everyone".

Seventeen days after the boys went missing and eight days after they were found, the round the clock mission began under dark skies and after 12 hours of heavy rains.

Four members of the “Wild Boars” soccer team, and their 25-year-old coach Ekaphol "Ake" Chantawong, had been left behind in the cave on Monday night after the second group of four boys was evacuated in another successful rescue effort.

They were in the cave with three Navy SEALs and a Thai doctor who had volunteered to stay with the boys since they were first miraculously found eight days ago.

The operation to save the final five began at 10.08am local time (1.08pm AEST).

The already-exhausted rescuers had to dig deep and plough on through soaring temperatures, rising humidity and thick mud.

As the minutes stretched into hours under the hot sun in this corner of north-western Thailand bordering Myanmar, hopes were rising that news of a third successful rescue by the so-called "all-star" team of Thai and international divers - which included as many as eight Australians in support roles - was imminent.

The success of the mission has drawn a line under an extraordinary rescue effort that has transfixed Thailand for more than two weeks and captured global attention for days on end.

In a briefing just before noon, local time, mission chief Narongsak Osottanakorn - who has become the international face of the rescue effort - said 19 divers (up from 18 on Sunday and Monday) would participate in the final push to bring the unprecedented operation to its conclusion.

Because of the heavy rains, which eventually eased in the afternoon, Narongsak said the decision had been taken to "not to waste time … for the third planned mission".

"We can do it [extract everyone] because we now have experience.

"From the first day to the second day we can do it two hours faster. The first day we spent 11 hours, yesterday we spent nine hours [from the start of the mission to the final rescue].

"Today [Tuesday] we might have to wait longer, but it will be worth the wait."

As a result of the increase in the number of people to be extracted, Narongsak had cautioned that Tuesday's mission would likely take longer. But "if everything goes right, we will see four kids and the doctor and the [three] SEALs that have stayed with the kids all come."

Earlier, Dr Jesada Chokedamrongsuk, the secretary of the Ministry of Public Health, provided a detailed briefing on the health of the eight boys who have already been rescued.

Two of the first boys had mild lung infections which could be pneumonia but, he said, most of the boys were "fine, normal" and had undergone a battery of tests, X-rays, and received vaccinations.

After initially being fed further power gel energy rations, the boys had moved to eating soft, boiled rice and had even asked for and received chocolate.

The second group of four were, if anything, in slightly better condition, though one boy had a very low body temperature and a slow heart rate.

Both groups were brought out of the cave with gauze over their eyes because of their prolonged stint 3.2 kilometres deep inside the cave, Dr Chokedamrongsuk said, and had inititally worn sunglasses at the hospital to soften their exposure to the light of the outside world.

The first group saw their parents and close family on Monday night, though through glass as they remained under quarantine, and the second group was scheduled to do so on Tuesday evening.

All of the boys were expected to remain in quarantine for up to a week before finally being allowed to go home and return to a life that will, likely, never quite be "normal" again.

The identities of the boys have not been confirmed by Thai authorities, but the first four boys brought out were aged 14 to 16 years old and the second group were 12 to 14 years old.