Updated 11:55

A diver volunteering to help get 12 boys and their football coach out of a cave complex in Thailand has said the rescue could happen "today or tomorrow."

Ivan Karadzic said he expected the mission to take place "very soon."

He also said the "mood has changed" among the rescue team after a former Navy Seal diver died while taking part in the effort.

"It makes us very sad," he said.

Death

Officials said Officials said Samarn Gunan had been returning from inside the waterlogged cave when his oxygen supplies ran out yesterday.

the former Thai Navy SEAL had been working as a volunteer and was placing oxygen tanks along a potential exit route.

"On his way back he lost consciousness," Thai SEAL commander Apakorn Yookongkaew said, adding that a friend had tried to help bring him out.

"But even though we have lost one man, we still have faith to carry out our work."

The body of Saman Gunan, a former Thai navy SEAL who died during the operation to rescue 12 boys trapped in a cave complex in Northern Thailand, 06-07-2018. Image: AP/Press Association Images

Race against time

Commander Yookongkaew said there was a "limited amount of time" to reach the boys and their coach.

Without elaborating, he said: "At first we thought that we could sustain the kids' lives for a long time where they are, but now, many things have changed."

If the rescue does happen soon, it will be partly because monsoon rain is forecast again from Saturday, and is likely to raise the floodwaters inside the cave.

Challenge

Mr Karadzic, a cave diver from Denmark, said the key challenge was that children were involved.

"Most cave divers will have training to rescue other cave divers," he explained. "But rescuing kids out of a cave - that is new to most of us."

It would be "very difficult," he said, adding: "I have zero experience with rescuing kids from caves. I don't think anybody has."

Mr Karadzic said the complex in Chiang Rai province was "not enormously challenging."

"The cave is very shallow - it's five, seven metres, so you can dive for a long time," he said. "The deeper you dive, the faster you consume the gas.

"But obviously the situation makes it incredibly challenging."

Water level

He said the flood water inside the cave complex was receding.

"When I was in there yesterday, it was going down about a centimetre or two per hour," he said.

Mr Karadzic has also been helping to plant diving cylinders along the 4km route to the boys and their coach.

It is not possible, he said, for divers who are pushing all the way through to the trapped group to carry enough air.

Dangers

Mr Gunan’s death highlights the perils of the operation to bring out the young boys and their 25-year-old coach from inside the Tham Luang Cave system.

The group has been trapped underground in Chiang Rai for nearly two weeks.

Thai authorities are racing to pump out water from the flooded cave where the group have been trapped since June 23rd.

Rescuers have managed to reduce water levels in the cave by around 40% but monsoon rains are expected on Saturday.

The boys, aged 11 to 16, and their coach were found on Monday - nine days after they went missing following a football game.

Cave dive

Parts of the passageway leading to where the group were found are still flooded all the way to the ceiling - leaving diving out of the cave the only option for survival.

Officials have said not all of those trapped may be extracted at the same time depending on their condition, and the boys have been practising wearing diving masks and breathing.

They are not thought to have attempted any practice dives.

The Thai Navy Seals are in charge of extraction plans, with the help of dive teams from Britain, America, Australia and Asia.