CHIANG RAI, Thailand (Reuters) - Eight of the 12 boys trapped with their soccer coach in a labyrinthine flooded cave complex in northern Thailand have been freed, authorities said on Monday, adding that the time for rescuing the others will depend on the weather.

The mission which started Sunday is a race against the clock with heavy rain expected this week which would again flood the tunnels with fast-flowing, rising water.

A crack team of foreign divers and Thai Navy SEALS guided four boys on Sunday and a further four on Monday through narrow, submerged channels from the muddy bank deep inside the Tham Luang cave where they had been stranded for more than two weeks.

“All four boys have arrived at hospital, all are safe,” Narongsak Osottanakorn, head of the rescue mission, told reporters of those freed on Monday.

Asked whether the remaining four “Wild Boars” team and their coach would come out at the same time in the next rescue effort, he said: “It depends on the plan... We have set the plan for four people so if they want to take five out (at the same time), then they need to change the plan.”

The operation on Monday went more smoothly than on Sunday and took two hours less as the practice became more refined, he said.

But he added rescuers may need more than 20 hours, to replan and replenish oxygen supplies, to be ready to mount the next mission.

Then it will depend on the weather. Heavy rain has struck the region intermittently over the last three days and further downpours could set back draining efforts at the cave.

“As all of us said, the main thing is we still need more than 20 hours to get ready,” Narongsak said. “And it is up to the environment. If the rain god helps us, then we may be able to work fast. But if the rain god doesn’t help, then it could be challenging.”

Prime Minister Prayuth Chan-ocha visited the cave to inspect the operation, with navy rescuers giving him a rousing cheer.

“The prime minister said that this kind of event should never happen again on Thai soil,” Narongsak said. “We should learn from this experience to prevent it from happening again.”

The team became trapped on June 23 when they set out to explore the cave after soccer practice and rains flooded the tunnels, trapping them inside.

British divers found the 13 a week ago.

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“RESCUE HAS BEEN IMMENSE”

But the efforts to rescue the boys - aged between 11 and 16 - have proved a monumental challenge. Some are not even strong swimmers, and have had to learn to dive in conditions that claimed the life of a former Thai Navy SEAL on Friday.

Thirteen foreign divers and five members of Thailand’s elite navy SEAL unit make up the main team guiding the boys to safety.

Slideshow ( 18 images )

Authorities have said the boys are being held close to divers and wear oxygen masks to enable normal breathing.

“The rescue has been immense,” said volunteer helper Somjit Saenset, 56. “I’m so happy the children came out safely. I want to send my moral support for all involved” in the rest of the mission.

Authorities have not confirmed the identity of the rescued boys. Some of the parents told Reuters they had not been told who had been rescued and that they were not allowed to visit the hospital.

Narongsak said the rescued boys had not been identified out of respect for the families whose sons were still trapped, adding that the boys were being kept away from their parents due to fear of infection.

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

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.

“I’m hoping for good news.”

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

(Graphic: Hope for the 13 trapped in Thai cave: tmsnrt.rs/2KR2zRj)