Key points:

Eight boys have now been extracted.

Four boys and the coach remain trapped in the cave.

The third phase of the operation to begin in '20 hours'.

Divers have rescued four more boys from a vast cave system in northern Thailand on the second day of a challenging mission, as the first four rescued boys recover in hospital.

The Thai Navy Seals leading the operation say eight boys have now been extracted from the cave and will now work to extract the four boys and their coach who remain trapped inside the cave system.

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Rescue mission chief Narongsak Osotanakorn said Monday's rescue operation was two hours shorter than the previous one after authorities reviewed the process to make it sharper.

He said the plan is to launch the third rescue mission within 20 hours, and he is hoping for “100 per cent success”.

But he could not confirm if all five would come out today. In a press conference last night he said it was up to the divers to decide whether it is possible to save all five at once, warning the plan worked best with four.

Thai Prime Minister Prayuth Chan-ocha earlier toured the rescue operations near the cave site, suggesting he may organise a party to thank foreign divers who have assisted in the evacuation operation.

After his visit, he went to Chiangrai Prachanukroh Hospital to visit the rescued boys.

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'Hooyah': Thai Navy Seals celebrate

The Thai Navy Seal unit celebrated the successful rescue of members of the Wild Boars football team, writing on their official Facebook page: "2 days, 8 Wild Boars. Hooyah."

The “Wild Boars” football team and their coach got trapped on June 23 when they set out to explore the vast cave complex after football practice and the tunnels became flooded.

British divers found the 13, huddled on a muddy bank in a partly flooded chamber several kilometres inside the complex, on Monday last week.

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How the operation on day two unfolded

The extraction of the four on Monday followed a similar pattern to the previous day, with the youngsters emerging in quick succession just before nightfall after navigating a treacherous escape route of more than four kilometres.

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.

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Authorities then struggled to determine the best way to save the "Wild Boars", with the group stuck on a shelf above the floodwaters in pitch darkness.

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.

But with oxygen levels inside dropping to dangerous lows and the prospect of heavy rains flooding the area completely, authorities decided they had to move quickly, and take the group out through the water-filled tunnels.

Dozens of foreign divers and other experts from around the world were brought in to help the rescue effort, working alongside Thai Navy Seals.

Deadly dangers

Rescue operations chief Narongsak Osottanakorn described Sunday's initial rescue bid as "D-Day" when it was launched, and there were fears that any one of many potential pitfalls could prove deadly.

Among these were that none of the boys had scuba diving experience and that they could easily panic while swimming underwater in darkness.

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Thirteen foreign divers and five members of Thailand’s elite Seal unit made up the main team guiding the boys to safety through narrow, submerged passageways.

The death of a former Thai Navy Seal diver who ran out of oxygen in the cave on Friday underscored the danger of the journey even for professionals.

But after the first four emerged late on Sunday afternoon, hopes began to rise of a fairytale ending to the ordeal.

First four boys stable

The first four boys in the football team were rescued on Sunday and are in a stable condition in hospital.

Each had to wear an oxygen mask to enable normal breathing, authorities said.

Narongsak said rescuers had to tighten a guide rope as part of their preparations for the second phase of the rescue on Monday.

There was no word on the condition of any of the people brought out on Monday.

Fried rice is the first request from rescued boys

"They (the first four rescued) are well and happy. This morning they complained that they are hungry and they asked for fried basil with rice," said rescue mission commander Narongsak Osottanakorn.

Pad Krapao is a basil rice meal with stir-fried pork or chicken, topped with a fried egg.

Narongsak said they will be "kept away" from physical contact with their parents until the risk of infection is over, he said, adding doctors will decide on family visits "at a distance or through glass".

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Authorities defend decision to withhold boys' identities

Narongsak defended the lack of public disclosure of the names of the boys who had already been guided to safety, saying it "will create ill feeling" if their names are released while others languish inside the cave.

Once again, despite all the rumours and speculation here in Chiang Rai, the names of the boys so far out of the cave have not been released. Authorities say that is “out of respect” for their families. Anything else until confirmed is conjecture. @SBSNews — Omar Dabbagh (@Omar_Dabbagh) July 9, 2018

“The four children are well at Chiang Rai Prachanukroh hospital. But they still need to be kept away from their parents and others due to fear about infection,” he said.

Medical teams previously said concerns included hypothermia and an airborne lung infection known as “cave disease”, which is caused by bat and bird droppings.

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He also urged the media to behave respectfully. More than 1000 journalists from across the world have descended on northern Thailand to report the story.

Anxious parents wait

Somboon Sompiangjai, 38, the father of one of the trapped boys, said parents were told by rescuers ahead of Sunday’s operation the “strongest children” would be brought out first.

“We have not been told which child has been brought out ... We can’t visit our boys in hospital because they need to be monitored for 48 hours,” Somboon told Reuters.

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“I’m hoping for good news,” he said.

The cave complex is off-limits during the rainy season, which usually runs from May to October when downpours can quickly flood it.

Relatives said the boys had been inside the labyrinthine complex during the dry season.

The president of football’s governing body, FIFA, has invited the boys to the World Cup final in Moscow on Sunday if they make it out in time.