The 13 bikes tied to the railings, and the small pairs of football boots strewn in the mud, are the only signs they were ever there. On Saturday morning, a young Thai football team and their coach entered the rocky tunnels of the Tham Luang caves in northern Thailand. When the monsoon rains fell, flooding the entrance, they were unable to get back out.

On Friday rescuers were still hopeful that the 12 boys, who are between 11 and 16, and their 25-year-old coach could be brought out alive. A possible new way into the caves was found on Friday morning, and water was being pumped out as quickly as possible. Thai authorities were also considering drilling a hole through the mountain into the cave, though it could take days or even weeks.

The rescue effort, which has gripped Thailand over the past week, has become an international operation. Cave diving experts have flown in from the UK and 17 US air force rescue and survival specialists have come over from Japan to join the 132 Thai army, navy and police officers working day and night to try to find the group.

The boys, members of Moo Pa academy, are believed to have crawled into the large series of caves through a narrow 15-metre tunnel that is now completely flooded due to almost non-stop heavy rain over the past six days.

They had cycled to the cave with their coach after football practice on Saturday morning. Since Saturday night, when they were reported missing, their relatives have gathered outside the cave’s entrance, which has become a churned-up mudbath.

Some of those waiting became so overcome with distress that they were taken to hospital. A vigil has been kept at the mouth of the cave, with prayers and songs, and Buddhist monks have tried to comfort the sobbing families.

Kham Chantawong, an aunt of the coach, Ekkapol Chantawong, said she knew he had visited the caves in the past and told the Guardian she was sure he would do anything to protect the boys.

“He took very good care of the kids,” she said, her face pale and pained. “They all got on very well together. The children never fought or even cursed at each other.”

The Thai prime minister, Prayuth Chan-ocha visited the scene on Friday. “They’re athletes. They’re strong,” he told the boys’ relatives in an attempt to comfort them.

Speaking to officials involved in the search, Prayuth said: “Whatever can be done, do it, the government will back it. I’m not worried about the work of the staff but I’m worried about time elapsed for those lost inside the cave.”

Prayuth Chan-ocha, the Thai prime minister, arrives at the cave site. Photograph: Linh Pham/Getty Images

The rain and rising water levels meant the search had to be paused for more than five hours on Thursday. The interior minister, Anupong Paochinda, described the difficult circumstances faced by the rescue divers.

“Divers are in dark areas that are not flat and there’s mud and rocks everywhere,” he said. “Therefore, for the Seal team that’s there, when they dive, sometimes one tank can only go as far as 30 metres and they have they have to turn back.”

The cave is one of Thailand’s longest, at six miles, and is a popular tourist attraction. A large sign by the entrance warns of the dangers of it flooding in the monsoon season, which runs from June to November.

Vernon Unsworth, a British diver who lives in Thailand, said he knew the cave intimately as he had been exploring its tunnels for six years. He said the conditions were “getting hostile”, and whether or not the boys were alive “depends where they are”.

He said: “If they’re in the right place they can survive for five or six days. But the water now, the floodwater, is getting higher and higher, so there will be a point in time where even this cave here, the entrance will close.”

Florian Witulski contributed to this report