The rescue operation to remove eight Thai boys and their coach who are still trapped inside a cave in northern Thailand has resumed on Monday, according to a Thai Navy official with knowledge of the operation, after four of the boys have been brought to safety on Sunday.

“The operation has begun and it is ongoing at the moment,” the navy officer told CNN. He said Monday’s mission involved the same divers who carried out Sunday’s treacherous operation, which took nine hours and led to the rescue of four boys.

Five ambulances were seen driving toward the Tham Luang Nang Non cave complex, and at least one helicopter was also seen heading towards the cave entrance.

It’s been more than 12 hours since a joint Thai-international rescue team successfully navigated flooded, narrow tunnels to bring out four members of the Wild Boars youth soccer team who went missing in the cave complex on June 23.

Officials said late on Sunday they’d need to pause the operation for at least 10 hours to fill oxygen tanks that had been depleted during the first phase of the rescue mission.

The four boys rescued are recovering in a nearby hospital and are yet to see their parents. A family member told CNN on Monday that they hadn’t been told which boys had been pulled out, and who is still trapped in the cave.

A relative of one of the Wild Boars soccer team says that the boys’ families have agreed to remain at the cave site until all of the boys and the coach are brought out of the cave.

Officials said on Sunday that it may “take days” to bring all 12 boys and their coach to the surface. Each boy is being accompanied by two divers and it takes hours to negotiate the flooded tunnels through the dark, murky water. Those still inside the cave are perched on a small muddy ledge 4 kilometres from the cave entrance, surrounded by floodwater and with a limited supply of oxygen.

The most dangerous part of the journey out of the labyrinth cave system is the first kilometre, in which they are required to squeeze through a narrow flooded channel. During this process, rescuers need to hold the boys’ oxygen tanks in front of them and swim pencil-like through submerged holes. Having completed this section, the boys are then handed over to separate, specialist rescue teams, who help assist them through the remainder of the cave, much of which they can wade through.

Rescuers are racing to beat the next downpour which could further complicate efforts to remove the boys, aged 11 to 16, and their 25-year-old coach. Rain began to fall late Sunday, and more rain is forecast throughout the coming days, which could undo ongoing efforts to drain the flooded caverns where the other boys remain trapped. On Monday, skies were largely clear over the site but rain has been forecast for at least the next three days.

Thailand’s Prime Minister Prayut Chan-o-cha was due to arrive at the site on Monday to oversee the remainder of the operation, according to government spokesman Lt. Gen. Sansern Kaewkumnerd.

Late on Sunday, nine hours after they entered the cave, elite divers emerged carrying four teenage soccer players who were quickly transferred to waiting ambulances to be taken to hospitals.

The four boys who were pulled from the cave are now recovering from their ordeal in a newly converted isolation ward at Chiang Rai Prachanukroh hospital. Doctors are monitoring them for any illnesses they may have picked up in the cave, and supervising efforts to build up their strength after more than two weeks with little food and no natural light.

“The next step is to make sure those kids and their families are safe because living in cave has a different environment which might contains animals that could transmit any disease,” a hospital statement said.

Thailand’s Health Secretary said last week that on arrival at hospital the boys would need to be quarantined for one to two days before being allowed to see their families. Visitors would need to wear sanitized clothes and stay two meters away from the children.

Twelve boys and their coach were discovered four kilometres into the cave complex by two British divers on July 2, nine days after they abandoned their bicycles and ventured inside only to become trapped by flood water. The rescue mission has been a huge operation, led by the Royal Thai Navy’s SEAL unit, and supported by a cast of hundreds.

Among those are US military partners, British cave diving experts – including the two men who first located the boys a week ago – and rescue workers from Australia, China and other countries.

Follow N1 via mobile apps for Android | iPhone/iPad | Windows| and social media on Twitter | Facebook.