Rescuers to drill hole in Thailand cave rescue operation

Thai rescue workers will drill a narrow shaft into a cave where 12 schoolboys and their football coach are believed to be trapped by flood waters, Thailand's interior minister said on Wednesday, the fourth day of a search that has been hampered by heavy rain.

The boys, aged between 11 and 16, and their 25-year-old assistant coach, went missing on Saturday after football practice when they set out to explore the Tham Luang cave complex, even though it is known to be prone to flooding in the rainy season.

Thai volunteers and military teams, including 45 navy SEAL unit members, have been deployed at the flooded cave complex, which runs 10 km (6 miles) under a mountain in the northern province of Chiang Rai.

"Tomorrow we can drill into the mountain but we won't drill too deep. Just enough to allow people through," interior minister Anupong Paochinda told reporters in Bangkok.

"We are trying every way to find the children," he said.

While distraught relatives and friends gathered at the mouth of the cave, rescue workers pumped out water, but persistent heavy rain has slowed their progress.

"Water is the biggest challenge. There is a lot of debris and sand that gets stuck while pumping," Army officer Sergeant Kresada Wanaphum said.

"We have to switch out units because there is not enough air in there," he said before heading back down the cave.

According to messages the boys exchanged before setting off, they had taken flashlights and some food.

Apart from some footprints and marks left by their muddy hands near the cave entrance, nothing has been seen or heard of them since Saturday evening, and the race to find them has dominated Thai news.

"I'm confident all are still alive," Prime Minister Prayuth Chan-ocha told reporters.

'Massive amounts' of water

Vern Unsworth, a British cave explorer based in Chiang Rai who has joined the search, said a lot of water was seeping into the cave from two directions.

"There is a watershed inside, which is unusual. It means there is water coming in from two directions," Unsworth said. "The biggest challenge is the water. Massive amounts."

Three divers coming from Britain were expected to reach Thailand on Wednesday evening to join the search, the interior minister said.

The US military has sent a search and rescue team at the request of the Thai government, Lieutenant Commander Nicole Schwegman, a spokeswoman for the US Indo-Pacific Command, said.

Thailand has asked the United States for survivor detection equipment, Tourism Minister Weerasak Kowsurat said.

"We hope this equipment will allow us to locate the spots that we need to reach faster," Weerasak told reporters.

A guide book described the Tham Luang cave as having an "impressive entrance chamber" leading to a marked path. It then described the end of the path and start of a series of chambers and boulders.

"This section of the cave has not been thoroughly explored. After a couple of hundred metres the cave reduces in size to a mud floored passage two metres wide and three metres high," author Martin Ellis wrote in "The Caves of Thailand Volume 2."

Nopparat Kantawong, the head coach of the team who did not attend practice on Saturday, said the boys had visited the caves several times, and he was hopeful they would stick together and stay strong.

"They won't abandon each other," Nopparat told reporters.

Sniffer dogs 

Exhausted relatives have been camped out near the cave's entrance for days desperately awaiting news about the missing team and their 25-year-old coach.

"I'm sad. I want (my son) to be safe, we've heard nothing from officials yet," Thinnakorn, the father of a 12-year-old in the cave, said.

Heavy rains overnight caused water levels to rise even as several high-pressure water pumps were installed inside the cave to drain the pools.

The flooding kept rescuers out of the tunnels as heavy rains fell overnight.

"The divers are now ready to go in as soon as the water drops to a suitable level," Thai NavySEAL said on their Facebook page Thursday. 

Border guards with police dogs scoured the site for new openings into the cave, which is several kilometres (miles) long.

Families brought clothing belonging to the kids to help the sniffer dogs find the team.

Search teams found three new holes this week, but only one of the chimneys was accessible.

The Tham Luang cave is a popular draw for local visitors during the dry season, though a sign at the entrance warns tourists not to enter during the wet season from July to November.