Medics appeared to remove one person on a stretcher but hid the person's identity behind multiple white umbrellas.
People across Thailand cheered the rescue operation, including at the Mae Sai Prasitsart school where six of the trapped boys are students. But rescue officials were also anxious about dwindling oxygen levels in the cave.
The team of 12 boys and their coach entered the cave system on June 23, when torrential rain caused the water level within the cave to rise rapidly, forcing them to venture deeper.
Monday's mission involved 18 divers from Thailand and overseas. The boys will remain in hospital for at least another week before being discharged to ensure they do not have any infectious diseases. "We will check later today whether their eyes have adjusted to light", said Dr Jesada. "But if the rain god doesn't help, then it could be challenging".
Mr Narongsak said about 100 people were involved in the operation on Tuesday, including the 19 divers newly sent into the flooded cave.
Last week, Musk said he was sending teams to Thailand from his private space exploration firm, SpaceX, and engineering firm, Boring Co. which is developing tunneling systems for transport projects.
The boys will remain in quarantine because of a fear of infection, and it's understood they have only been able to speak to family members through a window.
The painstaking rescue has required breaks to allow the group of 18 elite divers to rest and replenish the cave with oxygen for the remaining soccer team members, ABC News reports. A massive worldwide search operation was launched and it took 10 days to locate the boys, who had taken shelter on a dry slope, deep in the complex.
Thai officials say four boys were brought out of a flooded cave in northern Thailand on Monday.
Authorities have said extracting the entire team from the cave could take up to four days, but two straight days of success raised hopes that it could be done faster.
Thai Navy SEALS confirmed that the 9th boy had been extracted from the cave at 4:06 p.m.
But two of the boys freed from the partially flooded Thai cave have suspected lung infections, following their 16 day ordeal underground. Last Friday, one former Thai Navy Seal died while placing oxygen tanks deep within the caves.
Four more of the boys were carried on stretchers out of the labyrinthine Tham Luang cave on the Myanmar border on Monday, bringing to eight the total number brought out so far after two rescue pushes in successive days.
Authorities on Tuesday were planning for their final push.