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Rescuers worked through the night to try to reach a young football team and their coach Image Credit: AFP

MAE SAI, Thailand: 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" - published along with the other letters given to a diver on Friday and released the next morning on the Thai Navy Seal Facebook page.

Handwritten messages written by boys and their soccer coach who are trapped in the Tham Luang cave in Chiang Rai. Pic: Reuters

"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 the tunnels and hopefully allow them to escape by foot.

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

The 25-year-old coach of the footballers also sent a letter to the outside world, apologising to the boys' parents and thanking everyone for their moral 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.

Over 100 'chimneys' drilled into mountain in bid to reach trapped boys

More than 100 chimneys are being drilled into the mountainside in a frantic bid to reach a Thai youth football team trapped in a cave complex below, the head of the rescue mission said Saturday.

The unprecedented rescue effort is attempting to establish new ways to extract the boys from above, if the underground chambers flood and it is deemed too risky to evacuate the team by diving out through the submerged passageways.

"Some (of the chimneys) are as deep as 400 metres... but they still cannot find their location yet," Narongsak Osottanakorn told reporters, adding the mission lacked the technology "to pinpoint where they are staying".

"We estimate that (they) are 600 metres down, but we don't know the (exact) target," he said.

On the question of dipping oxygen levels in the cave, he said rescuers had managed to establish a line to pump in fresh air and had also withdrawn non-essential workers from chamber three - where the rescue base is - to preserve levels inside the cave.

The "Wild Boar" team have been trapped inside the Tham Luang cave complex for two weeks.

Coach 'apologies to the parents' of the boys

The 25-year-old coach of the football team has offered his "apologies to the parents" of the boys in a scrawled note released by the Thai Navy on Saturday.

Ekkapol Chantawong was for nine days the only adult with the children - aged 11 to 16 - until they were discovered on a muddy ledge by rescue divers on Monday.

"To all the parents, all the kids are still fine. I promise to take the very best care of the kids," he said in a note given to a diver on Friday but published on the Thai Navy SEAL Facebook page on Saturday.

"Thank you for all the moral support and I apologise to the parents."

It is the first message from the coach, whose role in the team's predicament has split Thai social media.

Many have lauding him after reports he gave his share of food to the kids before they were located and helped them get through nine days in the darkness.

Others have criticised him for agreeing to take the young boys into the cave during the monsoon season.

The group entered the cave on June 23 and got trapped as floodwaters tore in.

"To my grandma and aunt, I'm here. Don't be too worried. Please take care," he added in the letter.