Last Saturday, 12 young boys went to explore a cave with their coach after football practice in northern Thailand.

Their bikes were found abandoned at the entrance and shortly after, heavy rain sent torrents of water through the cave.

Over the past week, rescuers have been mounting an increasingly desperate search, in the hope the group are alive deep inside the cave but trapped by floodwaters.

Here's what the operation, in the jungle-covered hills around Chiang Rai, involves:

Expert divers

Thai navy divers been trying to access the deepest caverns of the Tham Luang Nang Non cave, the fourth longest in Thailand.

Four top British cave divers, along with some US military personnel, also joined the efforts.

The divers are swimming through tiny spaces and cannot risk going too far into flooded passages or they risk running out of air.

The search has been frustrated by rushing water and near darkness inside the cave. Debris and mud leaves divers with almost no visibility; they can only see a few centimetres in front of them.

It's been described as like swimming through cold coffee.

Pumps and drills

Powerful industrial water pumps, put in place to reduce the water level inside the cave, have struggled to combat relentless rains. With the entrance flooded, pumping was halted on Thursday and divers forced to stop their search intermittently.

Rescue efforts shifted to finding other ways to access - and reduce water in - the cave.

That has involved drilling through rock to drain water, so the divers could resume the search - although the thickness of the cave's wall has made this difficult.

Another option would be to drill into the cave to create a new route to try to reach the boys.

But finding an area on the densely jungle-covered and muddy mountainside for the heavy machinery required, while ensuring surrounding rock does not collapse, makes the idea of drilling a hole to access the cave an impractical one.

Drones and robots

Other technology has aided the massive human search effort which includes the military, police and hundreds of volunteers.

Drones equipped with thermal cameras have been flown over Tham Luang to detect possible access points. An underwater robot was deployed to send information back on the water depth and condition of the cave.

No technology exists to scan for people deep underground.

There are plans to send cameras down to try to work out the next step and potentially to make contact with the missing group.

Sniffer dogs

The animals have helped survey teams investigate the area above the cave complex, which is several kilometres long, searching for possible ways in. The dogs were brought to the site after smelling clothing belonging to the missing children, news agency AFP reported.

Relatives of the missing have camped outside the cave since they went missing on 23 June. Thailand's Prime Minister Prayuth Chan-Ocha arrived at the site to speak with them on Friday.