The Thai boys trapped in a cave with their football coach have sent touching letters to their families, urging them not to worry.

The letters – which included one from their football coach apologising for their plight –  were sent out with divers who have had to navigate dark and tight passageways filled with muddy water and strong currents in oxygen-depleted air.

One boy wrote: “I’m doing fine, but the air is a little cold but don’t worry. Although, don’t forget to set up my birthday party.”

Another, identified as Tun, wrote: “Mum and Dad, please don’t worry, I am fine. I’ve told Yod to get ready to take me out for fried chicken. With love.”

The rest of the scribbled letters on pages from a notebook struck a similar message of love for parents and telling them not to fret.

One boy named Mick wrote: “Don’t be worried, I miss everyone. Grandpa, uncle, mum, dad, and siblings I love you all. I’m happy being here inside, the navy SEALS have taken good care. Love you all.”

Ekapol Chanthawong, the coach of the Wild Boars football team, wrote: “To the parents of all the kids, right now the kids are all fine, the crew are taking good care.

“I promise I will care for the kids as best as possible. I want to say thanks for all the support and I want to apologise to the parents.”

The boys, 11 to 16, and their coach went exploring in the cave after a football game on June 23. Monsoon flooding cut off their escape and prevented rescuers from finding them for almost 10 days.

Rescuers said they will not immediately attempt an underwater evacuation because the boys have not yet learned adequate diving skills – but will if heavy rains recommence.

The rescue effort has already seen a disheartening setback with the death of a former Thai navy SEAL diving in flooded passageways to deliver oxygen supplies.

British divers Rick Stanton, a fireman in his fifties from Coventry, and John Volanthen, an IT consultant based in Bristol in his forties, were the first to reach the group. Images later showed that one of the boys was wearing an England football shirt

Asked at his news conference about bringing the boys out underwater, Chiang Rai Governor Narongsak Osatanakorn replied: “Not today because they cannot dive at this time.”

Narongsak said the boys were still healthy and have practised wearing diving masks and breathing in preparation for the diving possibility.

The path out is considered especially complicated because of twists and turns in narrow flooded passages.

The suggestion that the trapped team might have to wait months inside until a safe way out is available — as was the case in 2010 with Chilean miners trapped underground — has met with little enthusiasm.

Authorities continue to pursue an alternative option, which is finding a shaft or drilling into the mountain in which the cave is located to find a sort of back door entrance.

The death of the Thai diver, Saman Gunan, underscored the risks of making the underwater journey.

Gunan, the first fatality of the rescue effort, was working in a volunteer capacity and died on a mission to place oxygen canisters along the route to where the boys and others are sheltered, Thai SEAL commander Rear Admiral Arpakorn Yookongkaew said.

The strategically placed canisters allow divers to stay underwater longer during the five-hour trip to reach the stranded team.

Elon Musk, the entrepreneur behind the Tesla automobile and the SpaceX rocket company, said he would send engineers to help.

One of his enterprises is Boring Co., which digs tunnels for advanced transport systems and has advanced ground-penetrating radar.