A Chilean miner who spent 69 days underground has sent a message of hope to the 12 Thai boys who remain trapped inside a partially flooded cave in northern Thailand.

The miner, Mario Sepulved, who was among the 33 miners rescued from a Chilean mine in 2010, said he had “no doubt” the boys and their soccer coach could be saved in a video message posted on Twitter.

Thirty-three miners were shuttled to the surface up a narrow shaft in a purpose-built steel capsule after their copper and gold mine caved in on August 5, 2010, trapping them 625 metres below the ground.

In the first 17 days of the accident, authorities and the public believed they had been killed.

“I have no doubt that if the government of the country puts in everything and makes all possible effort, this rescue will be successful,” the Chilean miner said of the Thai rescue mission.

“May God bless you! We are praying for each of you, for each of the families and for these children.”

Chilean miner ‘Super’ Mario Sepulveda has sent a message to the 12 teens trapped in a cave in Thailand

Follow all the latest: https://t.co/Qt5vovt4OW pic.twitter.com/K6bYOi48Rf

— Sky News (@SkyNews) July 5, 2018

The 17^th Chilean miner lifted from the mine in the Atacama Desert, Omar Reygadas, has also emphasised with the Thai boys’ plight.

“It’s terrible for them – they’re little – but I believe that boys with a lot of strength are going to manage to be whole when they get out,” Mr Reygadas told the Associated Press.

The 64-year-old said it was difficult to provide any advice to the boys, but encouraged them to focus on “reuniting with their families.”

“They shouldn’t be ashamed to be scared,” he told the AP. “Because we were scared too. Our tears also ran. Even as adult men, we cried.”

Thai rescuers are working around the clock to find a way to extract the Thai boys, aged between 11 and 16, who have been now been trapped 800 metres to 1 kilometre below the surface of the cave for 14 days, including nine days without food.

The Chilean miners’ impassioned pleas of hope follow a former Thai navy SEAL dying early Friday morning trying to free the stranded soccer team from the Luang cave complex.

Former Sergeant Saman Kunan who was working alongside rescuers died after running out of oxygen, raising fear it will dangerous for the boys to attempt the risky dive out of the cave.

The round trip in and out of the cave to reach the boys can take a highly skilled diver about 11 hours.

Leading rescue commander, Chiang Rai Provincial Governor Narongsak Osottanakorn said rescue plans were dependent on the boys being able to navigate the treacherous cave network and dive to safety.

Mr Osottanakorn has warned forecast heavy rains could speed up the rescue mission.

“The boys’ conditions are not suitable… (they) cannot dive at this time,” Mr Narongsak told reporters, Channel News Asia reported.

“We’d like minimum risk. But we can’t wait until it rains heavily and worsens the situation. If that happens, we’ll need to reassess. The key thing is the kids’ readiness to dive.”