"No, not today," CNN quoted Narongsak Osottanakorn, the governor of Chiang Rai province, as saying to the media.

Officials are considering a rescue plan involving a "buddy dive" -- where an experienced adult diver would swim with each boy, according to a US official.

Thai divers would lead the mission and US divers would preposition oxygen tanks, the official said.

The rescue team also includes divers and workers from Australia, the UK and other parts of Europe and Asia.

The rescue mission could begin as soon as the weekend, but no decision has been made whether to proceed, the US official said.

On Friday, Thai Navy SEAL chief Rear Adm. Aphakorn Yoo-kongkaew said oxygen levels in the cave had dropped to 15 per cent, a level that one Thai medic said posed a serious risk of hypoxia, the same condition that causes altitude sickness.

Authorities had originally suggested the safest strategy for the boys, aged 11 to 16, and their 25-year-old coach, would be to keep them in the Tham Luang Nang Non cave complex until the monsoon season had passed in October and water levels had subsided enough for them to walk out.

More heavy rain is expected to fall over the weekend but the governor emphasized that rescuers would only try to free the team if the risk to their lives was minimal.

The boys went missing on June 23 after they had entered the cave complex during fine weather but became trapped when a sudden downpour flooded the narrow tunnels.

They were found on Monday night on a rock shelf about 4 km from the mouth of the cave by two British rescuer divers.

The cave complex is regularly flooded during the monsoon season which lasts until September or October.