The footage starts with a touching chorus of “thank you” from the boys, as the rescuers wade through the mucky water towards them.

The figures of the 13 loom eerily in and out of the torchlight, framed by the darkened walls of the cave.

Rescue of boys trapped in Thailand cave could take months

Some have their red football shirts pulled low over bare knees to keep out the cold – a sign of their unreadiness for nine days in the Tham Luang cave complex.

They look dazed but those who speak appear lucid, despite the long stretch without food.

The conversation continues with murmurs of Thai as the group confers, punctuated by reassurances from the diver.

One boy asks in halting English if they will “go outside”.

“No, no, not today … there’s two of us, you have to dive … we are coming, it’s OK. Many people are coming, many, many people, we are the first … many people come.”

The diver raises his fingers to show the group has been underground for 10 days, adding “you’re very strong”.

The diver gives the boys an extra light as the camera jags around and the audio fails, but steadies as one of the boys says “I am very happy”.

“We are happy too,” the diver adds.

“Thank you so much,” say the boys, unfailingly polite despite the urgency of their situation.

Alive: how one word lifted Thailand from the depths of despair, and lit faces with joy

They are from the Wild Boar football team and the first visual evidence of their survival lit up a country that has followed every permutation of a painstaking rescue that at times looked forlorn with floods rushing through the winding tunnels.

A three-member British team – Robert Harper, Richard Stanton and John Volanthen – arrived in Thailand last Wednesday to aid the search.

Two of the Britons reached the boys late on Monday, sparking joy in a country that has held its breath throughout the agonising rescue efforts.

Thai cave boys to get four months of food and diving lessons as focus shifts to tricky rescue

It was not immediately clear which diver speaks on camera. The team has avoided media all week, with Volanthen telling reporters only: “We’ve got a job to do” when he arrived at the site.

But elation at the survival of the group was tempered by the reality of a difficult extraction ahead and the possibility of psychological damage from the trauma of being trapped in the dark bowels of a mountain for a prolonged period.

“It’s hard to tell [the state of their mental health] from the clip,” said Wimonrat Wanpen, spokeswoman from the Mental Health Department of the Public Health Ministry.

“Their lives are getting much better after several days of crisis … but whether they will develop trauma depends on many factors.”

There are numerous options to get the boys out of the cave, but it will take time.

The underground complex in Chiang Rai province stretches for up to 10km. The British Cave Rescue Council estimates the boys are around 2km into the cave and between 800 metres and 1km below the surface.

Nine rescues that give hope to the boys trapped in Thailand cave

The safest option is to supply them in place, bringing them food and other supplies as they wait for water levels to drop, either naturally or by pumping it out, or until rescuers can find or create another exit.

But this could take anywhere from days to weeks to even months as the rainy season typically lasts through October.

The Thai navy is already doing this short-term, sending teams with high-protein liquid food to feed the boys, keep them company and explore the cave infrastructure where they are to ensure it is safe.

The Thai Meteorological Department forecasts light rain through Friday, followed by heavy rain starting Saturday and continuing through July 10.

This threatens to again raise water levels in the cave and complicate the supply missions or any extrication.

Along with the search efforts inside the cave, rescuers have looked for other possible ways into the caverns. Authorities said those efforts will continue.

Backhoes and drilling equipment were sent to the mountain, but creating a shaft large enough to extract the boys would be extremely complicated and could take a long time.

Diving would be the fastest, but arguably most dangerous, extraction method.

According to Anmar Mirza, national coordinator of the National Cave Rescue Commission in the US, “trying to take non-divers through cave is one of the most dangerous situations possible, even if the dives are relatively easy”.

By all accounts, the dives into the cave have been a challenge. Experts in caving and diving needed days to reach the boys.

Getting the boys out could go faster due to the installation of dive lines, extra oxygen tanks left along the way and glow sticks lighting the path.

Still the British Cave Rescue Council said: “Any attempt to dive the boys and their coach out will not be taken lightly because there are significant technical challenges and risks to consider.”