THAI rescue teams searching for 12 boys trapped in a waterlogged cave practised evacuation and medical procedures on Saturday, as the desperate search went into seventh day.

Caves may be magical places in the eyes of explorers, but as millions of Thais following the desperate search this week for a dozen schoolboys and their soccer coach trapped inside a massive flooded cavern have learned, they are also dangerous.

“Dark, silent and often impenetrable, caves are deeply mysterious and, as such, they have always had a strong fascination in human societies,” said Edoardo Siani, who teaches cultural anthropology at Kyoto University.

“They can also be inaccessible and lethal.”

The teams who have been searching for the boys, including Thai navy SEAL divers struggling through muddy water in pitch-dark chambers, have come up against that inaccessibility.

There has been no contact with the boys, aged 11 to 16, and their coach since they went into the cave last weekend and were hemmed in by heavy rains that blocked the entrance.

Those downpours have continued all week.

Medical teams staged drills on Saturday to prepare for their possible rescue as worries loomed over how the boys might be pulled out of the Tham Luang cave if and when they are found.

For Thais, Siani said, caves are like the otherworld — “a place that is at the same time powerful, alien, fascinating and scary.”

The soldiers, specialists and volunteers working at the cave may wonder what grim spirits have been pouring down near-constant rain, hindering the search and making the area a muddy mess that has turned even the simplest of tasks into a slog, as Associated Press photographer Sakchai Lalit documents in these images.

Through it all, though, hope remains that the boys and their coach can be found alive.

As the search for the boys hit its seventh day, attentions turned to their chances of survival inside a cave with little or no food and light.

The boys likely have access to freshwater — either dripping in though rocks or rushing in through the entrance — but experts warned that run-off water from nearby farms could carry dangerous chemicals or bacteria.

“If they drink the water in the caves and it makes them sick it could hasten the problem that they’re in, but if they don’t drink it then they’re also in trouble,” Anmar Mirza, co-ordinator of the US National Cave Rescue Commission, told AFP.

But even without food he said young, athletic boys could “easily live for a month or a month and a half” but the main challenge now would be mental resolve.

“The biggest issue that they’re facing right now if they’re alive is psychological because they don’t know at what point they might get rescued,” Mirza said from Indiana.

Thai Navy SEAL divers explored the entrance of the cave where muddy, fast-flowing waters complicated the search and water pumps were working around the clock to try and keep water levels down.

But it was a losing battle as a second chamber remained submerged. “Whenever the water recedes divers enter the cave immediately,” Thai Navy SEAL said on its Facebook page.

Several teams trekked into the thick jungle above the cave desperately looking for new openings that might lead to the trapped boys.

They found one “promising” entrance on Friday that led to a muddy chamber 40 meters (130 feet) down, Narongsak, the governor said.

But there was still no indication it linked to the main cave complex.

Officials said the boys know the site well and have visited many times before, buoying hopes that they might have trekked to a large airy chamber in the centre called Pattaya beach.