There are also reports the coach is nearing the entrance.
At least nine ambulances have been waiting at the site after the leader of the rescue operation earlier said the aim was to bring out all five of the football group 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.
Doctors were being cautious because of the infection risk and were isolating the boys in the hospital. They did get a treat, however: bread with chocolate spread that they'd requested.
The plight of the boys and their coach has riveted Thailand and much of the world — from the heart-sinking news they were missing to the first flickering video of the huddle of anxious yet smiling boys when they were found 10 days later by a pair of British divers.
They were trapped in the Tham Luan Nang Non cave that became flooded by monsoon rains while they were exploring it after a soccer practice on June 23.
At a news conference, Jedsada Chokdumrongsuk, permanent secretary at the Public Health Ministry, said the first four boys rescued, aged 12 to 16, are now able to eat normal food, though they can't yet take the spicy dishes favored by many Thais.
Two of the boys possibly have a lung infection but all eight are generally "healthy and smiling," he said.
"The kids are footballers so they have high immune systems," Jedsada said.
"Everyone is in high spirits and are happy to get out. But we will have a psychiatrist to evaluate them."
It could be at least seven days before they can be released from hospital, Jedsada told a news conference.
Family members have seen at least some of the boys from behind a glass isolation barrier, and Jedsada said doctors may let the boys walk around their beds Tuesday.
It was clear doctors were taking a cautious approach. Jedsada said they were uncertain what type of infections the boys could face "because we have never experienced this kind of issue from a deep cave."
If medical tests show no dangers, after another two days parents will be able to enter the isolation area dressed in sterilized clothing and staying 2 meters away from the boys, said Tosthep Bunthong, Chiang Rai Public Health Chief.
The second group of four rescued on Monday are aged 12 to 14.
Four ambulances and a convoy of other vehicles arrived at the cave site Tuesday morning to prepare for the third phase of the rescue.
Heavy rains in the morning cleared during the day, a reassuring sign for rescuers who have feared monsoon rains could imperil the rescue.
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