Rising water levels have interrupted efforts to find 12 teenagers and their football coach trapped in a cave in northern Thailand.
Pumping was halted and with the entrance flooded, Thai navy divers had to stop their search.
The boys aged 11 to 16 and their 25-year old coach entered the cave on Saturday and there has been no contact with them since.
The rescue operation is now focusing on finding another way into the cave.
Thai authorities said they planned to drill a narrow shaft into the mountain to create an alternative entry point.
It is not known, however, where in the cave the group are trapped nor even whether they are still alive.
Messages the children sent before setting off to explore the cave on Saturday suggest they had taken torches and some food.
Caving experts have told the BBC that as long as they are in a chamber above flood levels, they have a chance of survival.
The biggest dangers for the children would be hypothermia or lack of oxygen.
Tham Luang is Thailand’s fourth longest cave and known to be prone to flooding during the rainy season.
The teenagers and coach are believed to have been cut off from the entrance by rising floodwaters.
Rescue teams and volunteers have over the past days frantically tried to find a way into the cave, scouring the surrounding area for holes, but have failed to get through.
British caver Vern Unsworth who is based in Chiang Rai told Reuters that there were “massive amounts” of water seeping into the cave.
“There is a watershed inside, which is unusual. It means there is water coming in from two directions,” he said.
On Wednesday, three British cave divers arrived in the city of Chiang Rai along with some US military personnel, to help the efforts. They are expected to go into the cave once the main entrance is accessible again.
“Water is the biggest challenge,” Sgt Kresada Wanaphum in the Thai army told Reuters.
“There is a lot of debris and sand that gets stuck while pumping.”
As the search efforts enter their fifth day, Interior Minister Anupong Paojinda said officials were “confident the children are still alive”.
“They have food, they are skilful, we are confident they are safe.”