MAE SAI, THAILAND - The 12 boys trapped in a flooded cave in northern Thailand are being taught how to swim and dive on Wednesday (July 4) to prepare them for the possibility that they need to dive their way out, as rescuers continued to pump water from the cave before heavy rain falls as forecast over the coming days.

"Now we are teaching the children to swim and dive," Deputy Prime Minister Prawit Wongsuwan told reporters, adding that if water levels fell and the flow weakened, the boys, aged 11 to 16, would be taken out of the Tham Luang cave in Chiang Rai quickly.

"The water is very strong and space is narrow. Extracting the children takes a lot of people," Mr Prawit added.

Reuters reported that a group of about 30 divers in wetsuits was seen preparing kit and heading for the caves on Wednesday, accompanied by military personnel and a foreign cave expert.

The Thai authorities have appealed for donations of full-face scuba diving masks small enough to fit the boys in order to reduce the risk of their breathing apparatus coming loose as they travel through flooded passageways, the BBC reported.

Weerachon Sukondhapatipak, a deputy government spokesman, said there was much work to be done in preparing the boys for what could be a demanding task, and rescue teams should not be pressured to act faster.

"Some of them can't swim, so therefore it will take time for them to adjust," he was quoted by Reuters as saying.

"Officials would teach them how to move, how to dive, how to move their body under those circumstances."

The boys and their 25-year-old coach went missing on June 23. It is believed they entered Tham Luang when it was dry and sudden heavy rains blocked the exit.

They were found on Monday (July 2) more than 4km from the mouth of the cave after a frantic nine-day search by an international team including rescuers and divers from the United States, Britain, Japan and elsewhere.

British volunteer divers Richard Stanton and John Volanthen, who have day jobs as a fireman and Internet engineer respectively, negotiated a long and winding path through flooded caverns to find the 12 young boys and their coach.

A video released by the Thai Navy Seals on Wednesday showed two rescuers in wetsuits sitting on a elevated part of the cave beside the boys wrapped in foil blankets. They appeared to be in good spirits, occasionally laughing.

The boys would be brought out when they are mentally ready and physically fit for the potentially punishing journey of more than 4km to the mouth of the cave, the authorities said. Experts say divers have required three hours to reach the boys.

"All 13 don't have to come out at the same time. Who is ready first can go first," Chiang Rai Governor Narongsak Osottanakorn told reporters on Wednesday. "If there are risks then we will not be extracting them."

Parent 'not worried'

Somboon Sompiangjai, 38, said his son Peerapat, 16, was able to swim, adding that he was confident the SEALS' experience and professionalism would let them get the boys home safely.

"I am not worried if the kids have to swim and dive," he told Reuters. "I felt much better after seeing the clips with the children in good spirits, even though they were in there for 10 days."

The focus is now on monitoring water levels, rain forecasts and extraction procedures. As of late Tuesday, some 120 million litres of water had been pumped out of the cave.

"The first plan is to reduce the water level and get them out but if we can't, we will have a backup plan," Bangkok Post cited Navy Seal Chief Rear Admiral Aphakorn Yoo-kongkaew as saying earlier on Wednesday, referring to the diving gambit.

Oxygen tanks, food supplies

Rear Admiral Aphakorn said the whole team is now safely in the hands of seven Seal divers, a military doctor and a nurse from the Royal Thai Navy's underwater and hyperbaric medicine unit, who have volunteered to stay with them for as long as it takes, even months.

High-energy food and rejuvenating mineral salts were given to them so they can rebuild their strength after 10 days with almost no food or fresh water, and at least four days of food supplies have been prepared and 70 oxygen tanks sent in, the officials said according to Bangkok Post.

Officials on Tuesday dismissed as speculation reports that the boys could be trapped for up to four months.

Experts have cautioned that taking inexperienced divers through the dangerous corridors of muddy, zero-visibility waters would be very risky.

Thailand's Interior Minister Anupong Paojinda acknowledged that getting the boys to dive their way out could be risky, but added that rescuers have already formulated an evacuation plan, including assigning two divers to escort each of the boys.

"Diving is not easy. Those who have never done it will find it difficult, because there are narrow passages in the cave. They must be able to use diving gear. If the gear is lost at any stage, it could be perilous," the minister said according to Bangkok Post.

"As rain is forecast in the next few days, the evacuation must be sped up," General Anupong, the interior minister, said according to Bangkok Post.

"If the water rises, the task will be difficult. We must bring the kids out before then," he said.