The 12 boys and their football coach found after nine days stuck deep in a water-filled cave network in northern Thailand may be trapped underground for months.

The boys and their coach, who were missing since June 23, were found about 12.45am on Tuesday (AEST) by two British divers in a drama that has gripped not only Thailand, but the world.

But after the elation of the discovery in the flooded cave, Thai officials announced they would be dropping in four months’ worth of food for the boys, sparking speculation that it could be quite some time before they see daylight again.

Much-needed food and medical supplies – including high-calorie power gels and painkillers – were brought in on Tuesday for the boys, who had survived for almost 10 days with almost no food or fresh water.

Officials were also installing a phone line in the cave so the parents could have some way of reconnecting with their sons.

Authorities said the retrieval of the group would only occur once conditions were “totally safe”.

“[We will] prepare to send additional food to be sustained for at least four months and train all 13 to dive while continuing to drain the water,” Navy Captain Anand Surawan said, in a statement from Thailand’s Armed Forces.

The provincial governor of Chiang Rai, Narongsak Osotthanakorn said on Tuesday that it as hard as it was for rescue teams to hack and dive through the cave, bringing the boys back through the same terrain would prove extremely difficult.

“We won’t bring them out until we find a totally safe way,” said Mr Narongsak, who is officially in charge of operations at the cave.

Mr Narongsak was speaking less than 12 hours after he told the world that divers had located the team deep inside the Mae Sai district cave complex.

The boys, aged 11 to 16, and their 25-year-old coach disappeared when flooding trapped them after they entered Tham Luang Nang Non cave on June 23.

Navy divers and rescue workers entered a narrow passageway early on Monday after passing through a key chamber on Sunday. Its high, murky waters had previously blocked their progress.

Thai and British divers found the boys about 400 metres past the so-called Pattaya Beach area, where many of the rescue team had thought the boys might have sought safe ground.

When they reached the Pattaya Beach area and found it flooded, the rescuers decided to press in their search.

Mr Narongsak said teaching the group to swim and dive with breathing masks was one option to get them out. Finding mountainside shafts and other entrances was another.

The other option is waiting for the waters to recede – but that could take some time.

A US cave rescue expert Anmar Mirza told AAP “trying to take non-divers through a cave is one of the most dangerous situations possible, even if the dives are relatively easy”.

Thai omelette for first home-cooked meal

Relatives of the boys broke into cheers on receiving news the boys had been found.

Family members celebrate near Tham Luang cave after the good news. Photo: Getty

Aisha Wiboonrungrueng, the mother of 11-year-old Chanin smiled and hugged her family.

She said she would cook her son a Thai fried omelette, his favourite food, when he returns home.

Australian Foreign Minister Julie Bishop welcomed the news and commended the work of Australian rescuers who were part of an international contingent.

Two experienced British cave rescue divers, John Volanthen and Rick Stanton, were the first to reach the boys, according to Bill Whitehouse, the vice-chairman of the British Cave Rescue Council.

A video shot by rescuers in flickering torchlight revealed boys clad in shorts and red and blue shirts, sitting or standing on the rock above an expanse of water.

“How many of you are there – 13? Brilliant,” a member of the multinational rescue team says to the boys in English.

“You are very strong,” a rescuer says.

Watch the first footage of the boys’ rescue

-with AAP