MAE SAI, Thailand (AFP) - Thai rescue teams searching for 12 boys trapped in a waterlogged cave practised evacuation and medical procedures on Saturday (June 30), as the desperate search went into seventh day.

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, hampering the enormous rescue efforts to find the youngsters and their 25-year-old coach.

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.

Ambulances and helicopters were on standby for the drills Saturday morning at the bustling rescue site in northern Chiang Rai province.

"It's to set up a system to practise what to do until we can get them to hospital," Chiang Rai governor Narongsak Osottanakorn said late Friday.

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 fresh water - either dripping in though rocks or rushing in through the entrance - but experts warned that runoff 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, coordinator 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 metres (130 feet) down, Narongsak, the governor said.

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

"We have been rotating our staff into the chimney since yesterday, they are inside are still searching and we are waiting for their findings," Surachai Thathes, chief of the parks ministry rescue team for the north told AFP.

Teams of foreign experts, including more than 30 US military personnel, have descended on the remote mountainous site near the Laos and Myanmar border to join some 1,000 Thai rescuers.

Australians, Chinese and Japanese experts also joined efforts.

Stone-faced relatives kept vigil under a makeshift tent where monks are leading prayers.

Stretching 10km (six miles), Tham Luang with its complicated, snaking pathways, is one one of Thailand's longest and toughest caves to navigate.

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.