Scrawled deep inside a mountain in northern Thailand, heartwarming fragments of communication from trapped youngsters have reached families keeping vigil for two excruciating weeks at the entrance to the cave complex.

Players from the "Wild Boar" football team wrote short notes in the gloom, reassuring parents and relatives, making affectionate jokes and expressing hopes of being reunited in the near future.

"Love to Mum, Dad and my little brother," reads one note from 15-year-old Phiphat Photi -- who is better known as "Nick" -- given to a diver on Friday along with the other letters and released the next morning on the Thai Navy Seal Facebook page.

"If I get out, please can you bring me some grilled pork and vegetables?"

"I love you, Dad, Mum and my sister. You don't need to be worried about me. I love everyone!" wrote Pheerapat, nicknamed "Night", who turned 16 underground.

The letters provoked a surge of emotion from families, who first endured nine long days before their children were found dishevelled and emaciated but alive on Monday -- and now face an agonising wait for a dangerous evacuation.

"I am so happy to see his letter, his handwriting. I'm almost crying," Night's mother Supaluk Sompiengjai told AFP.

"It doesn't matter how long I wait as long as he is safe."

She may have some way to go. It is still unclear how the boys will be rescued from the range of dangerous options on the table, as the country holds its breath hoping for good news.

Teams are drilling multiple shafts through hundreds of metres of mountainside to try to reach them while industrial pumps are working round the clock in an attempt to clear water from the tunnels and hopefully allow them to escape on foot.

But the prospect of fresh monsoon rains and more flooding threatens to unpick the progress.

Attempts to install a phone line to allow the trapped boys to speak to their families have so far failed.

Divers had taken in a letter from relatives sending moral support to the boys and thanking 25-year-old coach Ekkapol Chantawong for looking after them.

Story continues

"From all the parents, please take care of all the children. Don't blame yourself," their letter to him read.

"We are not mad at you at all. We understand and are rooting for you. Thanks for helping and taking care of the kids." In a touching reply, the coach apologised to the boys' parents and thanked them for their support.

"To all the parents, all the kids are still fine. I promise to take the very best care of the kids," his note reads, sending his love to his own family and adding how much he is looking forward to eating his aunt's home cooking.