Mae Sai, Thailand: The underwater search for 12 children and their football coach trapped in a flooded cave in Thailand was halted as water levels rose amid relentless rainfall on Thursday.
But search teams, including three British diving experts and US military personnel, continued work above ground despite the setback, scouring the area for entry points to the cave where the team has been stuck since Saturday.
Officials prepared a massive industrial drill to create a new tunnel into the cave close to where the boys are believed to be trapped while drones were dispatched to find other openings.
Heavy rains overnight flooded a second chamber of the 10-kilometre long Tham Luang cave that is notoriously difficult to navigate, even among the most skilled divers.
"Under the current situation it's not possible to dive into the cave, they have to wait until the water recedes," Interior Minister Anupong Paojinda told reporters on Thursday.
"We are preparing to continue pumping the water out so the team can enter the cave," he added.
A team of American military personnel from the US Pacific Command, including pararescue and survival specialists, arrived at the site overnight to help rescue operations, according to embassy spokeswoman Jillian Bonnardeaux.
"Operators are trained in personnel recovery tactics and techniques and procedures," she told AFP.
"Essentially what they are looking at is assessing with the Thai authorities the potential courses of action and complementing the efforts underway."
Three British cave divers arrived at the site late Wednesday and tried to go into the cave but had to turn back because of heavy flooding.
They surveyed the site Thursday as officials said three other chimneys discovered earlier this week were shallower than hoped and did not lead to the cave's interior.
The young footballers, aged between 11 and 16, went into the cave with their 25-year-old coach and were trapped when heavy rains clogged the main entrance.
Around 1,000 Thai Navy SEAL divers, police, soldiers, border guards and officials have been mobilised for the around-the-clock rescue in a remote and mountainous part of Chiang Rai province near the Laos and Myanmar borders.
Tham Luang is one of the longest caves in Thailand and frequently floods during Thailand's monsoon season between July and November, rendering some of its narrow passages difficult to pass through.
There are several air pockets within the complex and the kids are believed to be in a large chamber in the middle of the cave.
But fast-running and murky flood waters have prevented rescue divers from reaching them and heavy rains continued to seep into the cave through narrow openings on the sides and through the main entrance.
"The water is like cafe latte, you can't see anything, and there's a very strong flow which doesn't make it easy," Ben Reymenants, owner of Blue Label Diving in Thailand, told AFP from Chiang Rai where he was assisting with the search.
As water pumps were set up in a scramble to drain the tunnels, experts assessed the scene for a possible location to drill a hole without collapsing the cave's walls - but said it would be a tricky task.
"It's difficult to drill vertically, if you go up the mountain and drill down there are high risks so we might drill from the the side to improve our chances of success," Suttisak Soralump, a geotechnical expert from Kasetsart University, told AFP.
Sniffer dogs were deployed in the morning after smelling clothing belonging to the kids that relatives brought over.
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 rainy months.
Officials said the football team and their coach Ekkapol Janthawong have been in the cave before and know the site well.
Photos on Ekkapol's Facebook page showed him with some young footballers in the cave in 2016.
The harrowing search has captivated Thailand, where local media is blanketed with coverage of the rescue.
A government spokesman said Thai Prime Minister Prayut Chan-O-Cha would visit the site on Friday morning.
"He wants to offer moral support to parents of the missing boys and the coach and all the officials working there," Sunsern Kaewkumnerd said.