A new video of a youth football team trapped deep inside a Thai cave has emerged showing the boys laughing and saying they are well after their discovery by divers nine days after going missing.

The Thai Navy SEAL footage shows 11 of the 12 boys and features a message to families waiting outside.

Each makes a traditional Thai greeting gesture to the camera before introducing themselves by nickname and saying "I'm in good health".

Several of the boys in the frame are wearing protective foil blankets and are accompanied by a smiling diver in a wetsuit, in video clips published on the Thai Navy SEAL Facebook page. 

They were accompanied by a 25-year-old coach, who went with the boys down the cave after football training on 23 June.

The one-minute video clip ends on a jovial note, with one of the 12 young footballers saying he was forgotten in the round of introductions, sparking laughter.

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The videos have delighted a Thai nation that has held its breath for a successful outcome to a complex rescue kilometres inside one of the country's longest caves.

But getting the boys out of the still submerged caves, with monsoon rains predicted to soon resume, is likely to be a protracted process and is fraught with risk.

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"We have to be 100% confident that there is no risk to the boys before we evacuate," said Chiang Rai provincial governor Narongsak Osottanakorn.

"We will take care of them like they are our own children," he said, adding efforts to install a telephone line failed yesterday, but food, medicine and relief gear continues to be ferried into the caves.

Authorities are also pumping out water round-the-clock, aware of the bad weather forecast in the days ahead.

In the video the boys, who have spent 11 nights underground, appear relaxed and much more alert than when they were when British divers found them late on Monday huddling on a muddy ledge above surging underground waters.

Outside the cave the mother of one of the boys cried as she watched the clip on a television screen, saying she was "glad" for a glimpse of her son.

"He is thinner" she said as she ran her finger over his image - a sign of the heartache the saga has brought to relatives of the trapped boys and their coach.

Several Navy SEAL divers have been deployed along with medics vowing to stay with the group while the challenging process of evacuating the "Wild Boar" team begins.

Thai authorities say the focus is now building up the boys' physical and mental strength after an ordeal that has left them emaciated.

Next they have three main options: diving out of the cave system, exiting through another hole if one can be found - or drilled - or waiting out the rainy season underground.

Experts say diving out is laden with risk, more so as the boys have never dived before and some may not be able to swim.

Areas of the cave remain submerged and navigating claustrophobic passages in murky rushing waters risks panic, even if the boys have ample equipment, expert support and a crash-course in how to dive.

The last option of waiting for the monsoon to abate, could be protracted as the monsoon begins to bite.

However, officials say they have stored food, medicine and equipment to last for up to four months at an underground base.