In a heartening message to families waiting in anguish outside, the Thai Navy SEAL footage features 11 of the 12-strong team, 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.

Their 25-year-old coach, who accompanied the boys down the cave after football training on June 23, is not heard in the footage, published on the Thai Navy Facebook page.

It is the second video to delight 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.

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

The boys appear relaxed and much more alert than when they were when discovered late Monday by British divers, as they took shelter from surging underground waters on a muddy ledge.

Outside the cave one of the boy's mothers teared-up as she watched the clip on a television screen, saying she was "glad" for a glimpse 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 13.

Several Navy SEAL divers have deployed along with medics, 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 my not be able to swim.

Areas of the cave remain submerged and the murky waters are very difficult to navigate, even if the boys are given good equipment and a crash-course in how to dive.

The last option could be protracted as the monsoon begins to bite and officials say they have stored food, medicine and equipment to last for up to four months at an underground base.