The operation to rescue the remaining eight boys and their football coach trapped in a flooded cave in Thailand resumed on Monday after four were brought to the surface yesterday.
The four unidentified boys freed were said to be in good health and recovering in hospital, although their parents reportedly remain unaware who has been rescued and who is still trapped.
The operation to rescue the group had resumed on Monday morning, Thai authorities said.
Heavy monsoon rains lashed the mountainous Chiang Rai region, where the Tham Luang Nang Non cave is situated, for several hours overnight.
The bid to rescue the schoolboys, aged between 11 and 16, was suspended on Sunday to replenish oxygen supplies and make new preparations.
Water levels will have an effect on the difficulty of the next stage of the rescue operation and it is not immediately clear how the rain overnight has affected levels inside the cave.
The heavy rain increases the risks in what has been called a "war with water and time" to save the boys.
Thailand's Meteorological Department said there was a 60% chance of rain on Monday, with thunderstorms forecast throughout the week.
Authorities have said the mission could take three or four days to complete.
On Sunday divers had to hold the first four boys close to their bodies to bring them out and each had to wear an oxygen mask to enable normal breathing, officials said.
The same divers who took part in yesterday's rescue will also conduct the next operation as they are familiar with the cave conditions.
The team is believed to include two elite British divers, Rick Stanton and John Volanthen, who were the first rescuers to reach the group.
The British Cave Rescue Council (BCRC) confirmed seven divers from the UK with "expertise in cave diving" are assisting.
Thailand's interior minister Anupong Paojinda said officials are meeting about the next stage of the operation and how to extract the remaining nine.
Anupong said divers need to place more air canisters along the underwater route to where the boys and their coach have been trapped since June 23. He said that process can take several hours.
He said the boys rescued on Sunday are strong and safe, but need to undergo detailed medical checks.
The head of the rescue mission, Narongsak Osottanakorn, said last week they would bring the fittest people in the group out first.
Somboon Sompiangjai, 38, the father of one of the trapped boys, said parents were told by rescuers ahead of Sunday's operation the "strongest children" would be the first to emerge.
"We have not been told which child has been brought out ... We can't visit our boys in hospital because they need to be monitored for 48 hours," Somboon told Reuters.
There were at least nine ambulances loaded with stretchers and blue oxygen tanks waiting in the cave area on Monday.
A source inside the Chiang Rai Prachanukroh hospital where the first four boys are being kept said their condition was "not bad", but doctors were watching for signs of emerging conditions such as hypothermia.
The boys went missing with their coach after football practice on June 23, setting out on an adventure to explore the cave complex near the border with Myanmar and celebrate a boy's birthday.
They were forced to go deeper inside the cave after heavy rainfall, becoming trapped.
They were discovered huddled on a muddy bank by British divers a week ago.
Samarn Poonan, 38, a former member of Thailand's elite navy SEAL unit, died on Thursday night as he worked underwater in the cave complex, laying oxygen tanks along a potential exit route.
Earlier in the week divers brought notes from the boys to their families, in which they urged them not to worry and asked to be taken out for fried chicken when they returned. The coach who led the boys into the cave has also apologised in a handwritten letter.