Divers trying to rescue 12 teenagers and their football coach trapped in a flooded cave in Thailand are getting closer to the cavern, where they hope the boys are sheltering. But there's a danger of the rescuers getting lost and running out of air while they search in total darkness. Oxygen tanks are being placed every 25 metres for emergencies. From the rescue site, CGTN's Martin Lowe has the latest.

The only illumination is the light they bring with them. Outside the range of their torch beams the darkness is total.

The boys may have carried torches when they entered the caves, but by now the batteries must have run out.

These pictures, taken by Thai navy SEALS, show the difficulties the rescuers face. In freezing water, they search by fingertip for a way through the caves. In sections hundreds of meters long, the tunnels are flooded from ground to ceiling.

Working around the clock the SEALs are battling hypothermia. They've appealed for space blankets in which to wrap themselves when they take a break from searching.

MARTIN LOWE THAM LUANG CAVES, CHIANG RAI "The more water that can be pumped out of the caves from outside, the better chance the SEALs have to reach the boys. But heavy rain causes the levels to rise quickly again - and it's forecast to return."

Heavy-duty pumps and pipes have been brought to the site from across Thailand. Water levels have been dropping, but that rain forecast is causing concern.

NARONGSAK OSOTTANAKORN CHIANG RAI GOVERNOR "The water pumping is in progress and is working well and the water is consistently getting lower."

There's been no contact with the 12 young footballers – aged 11 to 16 - and their 25-year-old coach since they entered the caves deep inside this mist-shrouded mountain on June the 23rd. Early monsoon rains have flooded the only route out.

This country's biggest ever rescue operation, aided by teams from China and around the world, is trying desperately to save them.

Martin Lowe, CGTN, northern Thailand.