Four of 12 schoolboys have been rescued so far from a flooded Thai cave after divers launched a daring and dangerous mission to free the children and their soccer coach, who were trapped underground for more than two weeks, Thai officials said.

“I have received information that six have exited the cave,” a senior member of the rescue team told Reuters.

Thirteen foreign divers and five members of Thailand’s elite navy SEAL unit are trying to bring the rest of the boys — some as young as 11 and weak swimmers — through narrow, submerged passageways that claimed the life of a former Thai navy diver on Friday.

A helicopter flew some of the boys to the nearby city of Chiang Rai where they were taken by ambulance to hospital.

Their ordeal has drawn huge media attention in Thailand and abroad, and getting the boys out safely could be a boost for Thailand’s ruling junta ahead of a general election next year.

“Today is D-Day,” Narongsak Osottanakorn, head of the rescue mission, had earlier told reporters.

Bursts of heavy monsoon rain soaked the Tham Luang Cave area in northern Chiang Rai province on Sunday and storms were expected in the coming weeks, increasing the risks in what has been called a “war with water and time” to save the team.

The boys, aged between 11 and 16, went missing with their 25-year-old coach after soccer practice on June 23, setting out on an adventure to explore the cave complex near the border with Myanmar and celebrate a boy’s birthday.

Rescuing them all could take three to four days and depended on the weather, an army commander involved in the mission had said earlier.

The rescue teams had rehearsed the plan for several days, Narongsak said, and had managed to drain the water level in the cave considerably, but needed to move fast.

“If we wait and the rain comes in the next few days we will be tired again from pumping and our readiness would drop. If that’s the case, then we have to reassess the situation,” he said.

An Australian doctor who is part of the rescue mission checked the health of the boys on Saturday night and gave the all-clear for the operation to proceed.

The boys were discovered by British divers Richard Stanton and John Volanthen on Monday.

Of the 13-strong foreign dive team — mainly from Europe — three were escorting the children, while the remainder were positioned along the dangerous first kilometer stretch, where the boys will have to navigate through submerged passageways in some places no more than 2 feet (0.6 meters) wide.

Thirteen medical teams were stationed outside the cave — each with its own helicopter and ambulance — one for each of 12 boys and their coach. After an initial assessment at the site, the plan was to airlift the boys to a makeshift helipad close to the Chiang Rai Prachanukroh hospital, some 70 km away.

A source at the hospital said that five emergency response doctors were awaiting the party and a further 30 doctors were on stand-by, adding that everyone was feeling tense.

“The teams here are happy the boys are being rescued but also anxious about the severity of the boys’ conditions. We’re under a lot of pressure,” she said, declining to be named because she was not allowed to speak to the media.

The area outside the hospital was cordoned off with police patrolling the area, said a Reuters reporter at the scene. Down the street, a loud speaker told vendors to “keep off the road” and to “not obstruct the transfer mission”.

Prime Minister Prayuth Chan-ocha, leader of the military junta that seized power in 2014, planned to visit the cave site on Monday, a government spokesman said.

His visit with relatives and rescue officials last week was criticized by some Thais as opportunistic as his government faced pro-democracy protests in the capital Bangkok in recent months.

UPDATED: In an earlier version of this story Reuters mistakenly reported the number of boys rescued. The current number is four.