By Agence France-Presse
There has been no contact with the boys, aged between 11 and 16, since they went missing with their football coach nine days ago.
The massive rescue effort has been hampered by heavy rains that flooded the Tham Luang cave in northern Thailand, blocking access to chambers where it is hoped the group will be found alive.
Divers took advantage of a brief window of good weather on Monday to edge further into the cave, with the water levels dropping slowly but steadily every hour thanks to round-the-clock water pumping.
Friends and teachers of the "Wild Boar" football team refused to give up hope of seeing the young players again.
Tilek Jana, whose friend Prajak is among the missing, said he was eagerly awaiting his return.
"Let him come and let's play (football) together, I miss him," he told AFP.
The principal of Mae Sai Prasitsart school, which is attended by six of the missing boys, said it had been a painful week.
"We chant and pray and send our support to them to give them power to wait for help to arrive," Kanet Pongsuwan told AFP.
Officials on Monday said the divers were less than one kilometre (0.6 miles) from an elevated area called Pattaya Beach where the boys are thought to be stranded.
"Everyone is tense," Chiang Rai governor Narongsak Osottanakorn told reporters late Monday.
But he struck a note of optimism in keeping with the official tone throughout the rescue saying: "We still believe we will find them soon."
Scores of divers -- including foreign experts -- have been sent into the cave with hundreds of oxygen tanks, establishing a base camp inside the chambers over the weekend.
Above ground several teams were drilling into chimneys that may lead to a new opening into the labyrinth of darkened tunnels.
"The deepest one is 200 metres and we will continue that operation. If we manage to get through the cave walls, then luck is on our side," the governor Narongsak said earlier.
Weary relatives have camped out at the cave's entrance for more than a week, desperately waiting for news of the boys, while the head of the Buddhist clergy has urged prayers from a nation fixated on the fate of the group.
- Race against time -
The football team and their 25-year-old assistant coach went into the cave on June 23 after a training session and got stuck when heavy rains cut them off from the entrance.
Rescuers found their bicycles, football boots and backpacks near the cave's entrance and discovered handprints and footprints further in.
But those are the only signs of the boys so far and no one knows if they are still alive.
They likely have access to fresh water inside the cave and officials believe they brought snacks with them and possibly headlamps too.
Even without food, experts have said young, athletic boys could survive for several weeks if they are not injured -- and don't attempt to escape through deep floods.
Yet it remains a perilously urgent rescue.
Officials have dropped survival kits with food, medical supplies and a cave map into a crevice in the hope that some of the relief will reach the boys.
At 10 kilometres long, Tham Luang cave is one of Thailand's longest and one of the toughest to navigate, with its snaking chambers and narrow passageways.
A sign outside the site warns visitors not to enter the cave during the rainy season between July and November.