CHIANG RAI, Thailand - The third phase of the high-risk rescue operation for the boys and their coach trapped in a cave in Thailand began Tuesday. Four boys were rescued Sunday and an additional four emerged Monday.

Rescuers have been taking the strongest boys out first. It may seem counterintuitive, but the reasoning for that was that officials want the boys who have the best chance of surviving to get through the escape route first.

The boys, ages 11-16, and their 25-year-old coach became stranded when they went exploring inside after a practice game. Monsoon flooding blocked off their escape and prevented rescuers from finding them for almost 10 days.

The ninth, tenth, and eleventh people to be rescued from a cave in Thailand, where a soccer team and their coach became trapped due to rising floodwaters, were seen being carried out to a field to be transported to the hospital Tuesday.

Divers were carrying out what they hoped would be the final operation to save the remaining four boys and their soccer coach, who have been trapped for more than two weeks.

Officials in the previous two days of the rescue mission did not confirm rescues until the day's operations were over.

Third phase of rescue mission is underway

An ambulance was seen leaving the site of the Thai cave Tuesday where divers were carrying out what they hoped would be the final mission to rescue four boys and their soccer coach still trapped deep inside.

At least nine ambulances were waiting at the site after the leader of the rescue operation said Tuesday's aim was to bring out the boys and their soccer coach, as well as a medic and three Thai Navy SEALS who have been with the trapped boys. Officials have generally waited hours to confirm rescues.

"All five will be brought out at the same time today," the Thai official overseeing the rescue mission, Narongsak Osottanakorn, said to cheers from reporters and rescue workers.

Thai health officials: Rescued boys are in good health overall

All eight boys who have been rescued are in good health overall, Thai health officials said Tuesday. The children were given antibiotics, but there were no significant diseases or abnormalities have been found.

But Thongchai Lertwilairatanapong, inspector general of the public health ministry, said preliminary blood checks indicated "all kids showed signs of infection," according to Reuters. They boys will be in the hospital for a week.

Officials said the boys asked if they could attend the World Cup, but doctors told them they would have to watch it on television. They are expected to spend a week in the hospital.

Three ambulances seen entering cave site

Three ambulances along with cars, hummers and soldiers have been seen entering the cave site. Heavy rains lashed the northern Thai region late Monday and a steady downpour has continued Tuesday.

After divers brought out four of the boys Monday evening, authorities indicated the rescue operation would continue for a third day. But they also warned heavy rain could hamper their efforts.

The rescue missions take nearly half a day to complete. Monday's mission took about nine hours, two fewer than Sunday's.

Elon Musk says he has visited the cave rescue site

Elon Musk says he has visited the flooded cave in northern Thailand where a youth soccer team became trapped and has left a mini-submarine there for future use, but it seems the rescue team may not be able to put it to use.

The tech entrepreneur tweeted Tuesday morning he'd "Just returned from Cave 3," referring to the rescuers' command center inside the sprawling cave. He posted photos of the cave interior and a video showing people working their way through chest-high water.

He also posted a video on Instagram.

A post shared by Elon Musk (@elonmusk) on

Musk has offered a "kid-sized" submarine, named Wild Boar after the kids' soccer team, to help in the rescue operation. He posted videos of the sub being tested in a swimming pool in California with simulated narrow passages like the cave.

Later on Tuesday, however, BBC News quoted head of the rescue mission, Narongsak Osotthanakorn, as saying "the equipment they brought to help us is not practical with our mission."

"Even though their equipment is technologically sophisticated, it doesn't fit with our mission to go in the cave," Osotthanakorn, who is the regional governor, said according to the BBC.

Here's how the dangerous rescue mission works: Each of the boys wears a dive mask as they enter the murky water. The children can barely see anything in front of them.

They are led by a diver who is carrying their oxygen tank and guided by a rope. Another diver follows them from behind.

This graphic illustrates the escape route that rescuers are taking to free 12 boys and their soccer coach from a flooded cave in Thailand.

The entire journey covers about two-and-a-half miles through both deep water and steep climbs.

The biggest concern is a "pinch point" in the cave that is just 15 inches across.

In that area, the boys have to separate from the divers in order to fit through and reach a small patch of dry land before going back down into the water.

New images from inside the cave:

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CBS News obtained new images from inside the rescue operation showing the sheer scale of this effort. The images show rescuers charging through the flooded cave, but also exhausted and sleeping on the rocky floor.

An international army formed to first find and then save the lives of these 12 young boys and their coach.

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Officials say medical evaluations of the boys will likely take three to five days but could take as long as seven, CBS News correspondent Anna Werner reports from Chiang Rai.

The first issues doctors will be looking for are dehydration and malnutrition. During the two weeks the boys were in the cave, they didn't have proper nutrition or exercise. After they were rescued, some of the boys asked for a Thai dish of meat with chili and basil.

The hospitalized boys are being kept in isolation, due to fear of infection.