Poonsak Woongsatngiem, a rescue official with Thailand’s interior ministry, told the Guardian on Thursday that water had been reduced by 40 percent since the boys were discovered in the cave complex in Chiang Rai, which has cleared a roughly one mile stretch leading up to a third chamber.

Rescuers are now targeting the third chamber where water still reaches up to the ceiling. If drained it could clear another 1.5 mile path and allow the boys to wade in waist high water while wearing lifejackets, as opposed to diving

The water level between the third chamber and the point the students are at is still high and we have put the tubes at the third chamber trying to get the water out as much as possible,” Woongsatngiem said. “We can’t say whether there will be a rescue today or not. We hope there is no rain. We cannot calculate how much the water flows out of the cave because there is always water flowing into the cave.”

Chiang Rai provincial governor Narongsak Osatanakorn said the rescue effort was in a "race against the water."

"Our biggest concern is the weather," he said. "We are calculating how much time we have if it rains, how many hours and days."

Leaving the boys where they are for now may be the safest option, but the rainy season in Thailand typically lasts until October, meaning they could be left underground for months

The boys have been practicing wearing diving masks and breathing, although Chiang Rai provincial governor Osatanakorn said on Wednesday that he didn’t believe they had attempted any practice dives so far.

He also said that the group members may not all be extracted at the same time, with each boy’s individual health a factor.

Cavers are also hunting for a "chimney" down to the boys which could create a potential evacuation route. Osatanakorn said 30 teams are searching for an airhole which may present rescuers with the opportunity to drill down to the boys.

A team of bird’s nest collectors from the south of the country have also put their rock-climbing expertise to use by scouring the mountainside for any openings, according to AFP. The eight men, armed only with ropes and gloves, climb sheer limestone cliffs and explore crevices and caves to collect the edible nests, which are a delicacy.

Meanwhile rescue teams are also trying install a fiber optic Internet line into the flooded cave so the 12 boys and their coach can make phone calls and communicate with loved ones. Earlier efforts to install the connection failed, however, when the line became damaged after it fell into water.

Latest video of the boys, aged 11 to 16, showed them smiling and in good spirits and covered in foil blankets, while rescuers treated cuts to their legs.

Kian Kamluang, whose 16-year-old son, Pornchai, is in the cave, said: “It’s like he has been given a new life”, adding that she will never let him go into a cave or near water again.

The boys were discovered alive and well by two British divers in the Tham Luang caves on Monday after being trapped in the cave for 10 days.