Cave rescue to start if heavy rains begin

Rescuers say the trapped schoolboys don't yet have enough diving skills for an underwater rescue

The rescue of a dozen schoolboys and their soccer coach who have been trapped in a Thai cave for two weeks will be held off for as long as possible or until heavy rains begin.

The official in immediate charge of the operation, Chiang Rai Governor Narongsak Osotthanakorn, says conditions in the cave continue to improve and a rushed operation to free the 13 people will not be undertaken unless necessary.

"If there are heavy rains, and the situation is not good, we will try to bring them out sooner," he told a media briefing late on Friday.

Narongsak expressed concern that the boys, aged between 11 and 16, and their 25-year-old coach were not skilled enough at the moment to attempt to scuba-dive out despite the group being in relatively good health and spirits.

He also said decreasing oxygen levels in the cave posed a risk that would also factor into bringing the rescue operation forward.

Heavy rain is forecast over the weekend after several mostly dry days and could cause flooded areas in the cave to rise again.

Divers assisting with rescue planning remain optimistic an underwater operation is still possible despite an ex-Thai navy SEAL dying while bringing oxygen into the cave.

Citing "daily progress" in conditions inside the cave, Danish diver Ivan Karadzic said he believed the Thai children and their coach would be able to swim out.

"The most difficult thing is that they're kids," he said.

"They don't need to do a cave course. They need to learn some basics. I believe the training has already started."

"I believe it's possible for all 13 to come out," he replied when asked about some children being more physically ready for the journey that takes SEAL experts up to six hours to complete.

Early on Friday, former Thai navy SEAL Saman Kunan died while placing oxygen tanks in the cave in preparation for the rescue mission.

It's unclear if the oxygen tank carried by the 37-year-old malfunctioned or simply ran out.

Complicating matters inside the cave is the temperature of the water, which Karadzic said was 20C, cold enough that "even in your wetsuit you get chilled".

Workers have been working to install a 4.7km pipe to bring oxygen into the deeper recesses of the cave complex.

On Friday, rescue teams continued to scour the mountainside looking for possible chimneys or areas where workers could drill into the cave's roof and then possibly airlift the boys out.

The group visited Tham Luang-Khun Nam Nang Non Cave, 1000km north of Bangkok, on June 23. A flash flood blocked their way out.

The discovery of the missing group by British divers late on Monday brought relief to their families.

A dozen Australian defence and police specialists have joined in the rescue.