CHIANG RAI - More than 100 shafts are being drilled into a mountainside in Northern Thailand in a frantic bid to reach a group of young footballers and their coach trapped in a cave complex below, the head of the rescue operation said on Saturday (July 7).

Mr Narongsak Osottanakorn confirmed that an extraction is possible within "one or two days", as rescuers raced against time before expected heavy rains set in.

"Everything is a race against time," said Kamolchai Kotcha, an official of the forest park where the cave complex is located. His team would camp out on the hill to try and finish its work before the rain came, he said.

The rescuers of this unprecedented effort are trying to establish new ways to extract the boys from above, if the underground chambers flood and it is considered too risky to evacuate the team by diving out through the submerged passageways.

"Some (of the shafts) are as deep as 400 metres... but they still cannot find their location yet," Mr Narongsak 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.

Mr Chongklai Worapongsathorn, deputy director-general of the Department of National Park, Wildlife and Plant Conservation, said many holes have been drilled and many teams have been sent out to look for more, but so far, none of them can lead to where the boys are.

Noting that a means to free the boys has not been decided, Mr Narongsak said that the water levels from the cave entrance to chamber three - where the rescue base is - is currently low enough for personnel to walk through.

However, he added, the water from chamber three to the T-junction all the way to where the boys are is still high.

Rescuers have been pumping water around the clock in an effort to drain the deluged cave enough so that the boys can safely exit the cave.

"During the peak of the rainy season, we are worried that the area where the boys are can be inundated or can be left at just 10 sq m. If there is more rain, there is more risk."

Given the risk of the oncoming rains that could undo the drainage efforts, Mr Narongsak said the conditions were now ripe for the boys to be evacuated.

While oxygen levels have stabilised after dropping on Friday due to the large number of people working in the cave, Mr Narongsak said rescuers had managed to establish a line to pump in fresh air and had also withdrawn non-essential workers from chamber three to preserve levels inside the cave.

But there were now concerns that carbon dioxide levels in the cave could rise and pose a risk to the group. "Now and in the next three or four days, the conditions are perfect (for evacuation) in terms of the water, the weather and the boys' health," Mr Narongsak told reporters. "We have to make a clear decision on what we can do."

On the condition of the stranded boys, he said: "They have been given high-protein, high-energy food which is not meant to fill their stomachs and some of them are still weak. However, they are all healthy and can communicate clearly and joke and play among themselves."

On Saturday morning, the Thai Navy SEAL posted on its Facebook page scribbled notes by the youngsters.

"Father and mother, please don't worry about me. I am fine. Please take me to eat fried chicken after this. I love you," wrote 11-year-old Chanintr Wiboonroongruang (Titan).

Pipat Potiayu, 15, wrote: "I love you mom and dad and I want to eat pork shabu."