Four were rescued Sunday and another four were rescued on Monday.
Narongsak also said Monday that the condition of the five remaining people in the cave is "still good". "From what I've seen in the clip, they did look skinny", he said.
Four boys were extracted on Monday, the Royal Thai Navy has confirmed. He is still believed to be one of the nine inside the cave. "Four boys were brought out today". Some stretches of the Tham Luang cave are more than 10m (33ft) high, while others are a tight squeeze through water-filled passages.
Oxygen depletion is also a problem as more people crowded into the small area where the soccer team took refuge.
The rescue operation began Sunday and has been progressing rapidly.
Experienced cave rescue experts consider an underwater escape a last resort, especially with people untrained in diving, as the boys are.
After Musk received an outpouring of gratitude for his rescue plans, he replied: "Thanks, we've not done anything useful yet".
Rescuers had planned to take a 10- to 20-hour pause in the rescue efforts to replenish the cave with oxygen and give the team of 18 divers leading the boys on the hard journey a chance to rest.
"The operation went much better than expected, " Chiang Rai acting Gov. Narongsak Osatanakorn, who is overseeing the mission, said Sunday night. The death of a former Thai Navy SEAL diver on Friday, who ran out of oxygen, underscored the danger of the mission, which has been termed a "war against time and rains". One local official told Fox News on Monday that they are hoping to finish the job in three days, suggesting that they may plan to extract the remaining trapped boys and their coach on Tuesday, which may allow time for rescuers to test out Musk's invention. They are all members of a youth soccer team called the Wild Boars.
According to NBC News, the twelve boys, ages 11 to 16, and their 25-year old coach entered the caves two weeks ago but were trapped after rain caused flooding.
The unidentified boys were carried out of the Tham Luang Nang Non cave on stretchers and into ambulances Monday before being airlifted to the Chiang Rai Pranukroh Hospital.
Thai authorities say four more boys have arrived safely at the hospital following their rescue after having been trapped in a flooded cave for more than two weeks.
But with oxygen levels inside dropping to risky lows and the prospect of heavy rains flooding the area completely, authorities decided they had to move quickly, and take the group out through the water-filled tunnels.
Authorities spent hours replenishing air tanks along the cave's treacherous exit route.
Four boys were retrieved from the cave Sunday, with Narongsak noting that the healthiest boys were removed first. Efforts to pump water out of the cave have been set back by heavy downpours. However, they ended up starting the rescue effort a few hours earlier than planned.
The photo, posted on the Thai Navy SEAL page on Sunday, and has received over 60,000 shares.
"Very fearless and talented people!" he tweeted.