CHIANG RAI - Eight boys from a Thai youth football team trapped in a cave in northern Thailand have been rescued, the Thai Navy Seals confirmed in a Facebook post on Monday (July 9) evening.

"2 days, 8 Wild Boars. Hooyah," the Thai Navy Seals said in a post on their official Facebook page, referring to the boys and their coach by the name of their football team.

At a press conference on Monday evening, the head of the rescue mission Narongsak Osotthanakorn said the health of five people still trapped inside the cave was "still good", after also confirming that four more boys were brought out safely from the cave complex.

"We have helped four more children today," said rescue chief Narongsak. He said rescuers would resume an operation to extract a remaining five people in about 20 hours' time. "The health of the remaining five people inside the cave is still good," Narongsak added.

The eighth boy was seen being carried out at 7pm local time (8pm Singapore time) on a stretcher from the flooded Tham Luang cave on Monday, shortly after three other members of the football team emerged safely when the daring rescue mission resumed earlier in the day.

A team of international and Thai divers entered the cave this morning again, after pulling off a successful operation on Sunday (July 8) that helped rescue the first four of the 13 people trapped.

This brings the current number of rescued to eight, while four more boys and their 25-year-old coach remain stranded in the cave. Rescue operations are also reportedly completed for the day, Reuters said.

The sixth and seventh boys who emerged at around 6.30pm local time were reportedly sent to a medical facility onsite, shortly after they were also carried out on stretchers from the cave.

Earlier at around 5pm local time, a fifth boy was successfully rescued, according to local media.

It is understood that the boys will be flown by helicopter to a hospital in nearby Chiang Rai, where their four other teammates rescued on Sunday are receiving medical attention.

According to a CNN eyewitness who is part of the rescue operations stationed at the entrance of the cave, the four boys rescued today were wearing full face diving masks while they were carried out to the makeshift hospital nearby. They were also wearing dive suits while being carried on stretchers, CNN said.

Thailand's Prime Minister Prayut Chan-o-cha has delayed a planned visit to the site so as not to disrupt the rescue operation, the Guardian reported. He had been due at the site at 6pm local time but instead arrived at a Chiang Rai airport at 7.45pm.

Earlier in a daily press briefing held by Mr Narongsak Osottanakorn, the head of rescue mission, he said that "good news can be expected in a few hours".

"We assessed everything...the way the ropes are placed so the boys can push themselves up. We can confirm that the water level is manageable, even if it rains and that we have enough personnel to do the job," he said.

The four boys, rescued on Sunday, were flown by helicopter from the Tham Luang cave to the Chiang Rai Prachanukroh hospital, located at the heart of Chiang Rai province, about 70km away.

"The four children are fine. The children complained that they were hungry and wanted holy basil stir-fried rice," Mr Narongsak told reporters on Monday, referring to a popular Thai dish.

At the hospital in Chiang Rai, green canvas sheets had been put up to block the entrance from view. Ambulances were on standby to receive the next batch of boys who are expected to be plucked from the cave, Reuters said.

Twelve boys, aged between 11 and 16, went missing with their 25-year-old coach after they entered the Tham Luang cave on June 23.

Four boys were rescued on Sunday (July 8) before the rescuers announced a suspension of 10 to 20 hours to allow the divers to rest and to replenish oxygen tanks and supplies in the complex cave network.

Mr Narongsak explains that while heavy rains are forecast this week as the monsoon season kicks in, round-the-clock drainage of water from the cave is working very well. Intermittent heavy downpours have drenched the area since Sunday afternoon.

A 90-member rescue team, made up of 50 foreign and 40 Thai divers, are racing against time to get the remaining eight boys and their football coach out of the cave complex in a forest park near the Thai border with Myanmar.

Eighteen divers, including five Thai Navy Seals, were deployed during Sunday's rescue. Ten of them dived during Sunday's operation. Three of them were technicians.

Asked whether the identities of the boys rescued on Sunday can be released, Mr Narongsak said naming the boys would be against medical ethics. The authorities also have to think about the boys' families, he added, saying it "will create ill feeling" if their names are released while others languish inside the cave.

The drainage of water and lower-than-usual rainfall during this period have sent water levels inside Tham Luang cave to the lowest in days, rendering most parts of a 5km escape route "walkable".

Divers reportedly had to work through the night to replace air tanks and supplies along the route that cuts through the cave's dark and narrow passageways before restarting the rescue operation at 11am local time on Monday (July 9).

Thailand's interior minister Anupong Paojinda said on Monday the same team of divers will be tasked with Monday's operation as they are familiar with the cave conditions and know what to do.

Parents of the remaining eight boys are waiting anxiously outside the cave entrance.

"I am still waiting here at the cave, keeping my fingers crossed to see whether my son will be one of those to come out today," Supaluk Sompiengjai, a mother of Pheerapat - known by his nickname "Night" - told AFP.

"We heard four boys are out but we do not know who they are. Many parents are still here waiting. None of us has been informed of anything." But she added she was "happy" at the prospect of seeing her son again.

Mr Anupong said the four boys rescued on Sunday "are strong and safe" but would need to undergo detailed medical check-ups.

Dr Thongchai Lertwilairattanapong, an inspector for Thailand's health department, told Thai daily newspaper Kom Chad Lek the boys should be able to see their families later on Monday, but added that there must not be any physical contact.

"No hugging or touching and they need to leave a one to two metre distance from the patients until the results of their blood tests come back," he said. Doctors are checking to make sure the children are free from serious infections such as leptospirosis and meliodosis.

Reports say the boys have undergone blood tests, lung X-rays and urine tests. One of the concerns is refeeding syndrome, a potentially fatal condition which involves the shifts in the body's fluids and electrolytes. It is caused when people start eating after a period of malnourishment.

One of the four freed boys is said to be in poor health and requires "close monitoring". A source told The Nation newspaper his health has improved after he was admitted to hospital on Sunday night.

It is believed that rising water levels from sudden downpours on the day they entered the cave forced them to seek refuge on higher ground further inside the cave. They were found nine days later, huddled together on a tiny ledge some 5km from the cave's mouth.

Mr Narongsak, who has become the face of the rescue mission, said at a press conference on Sunday night that the first operation was "more successful than anticipated".

He said it has to put on hold to allow time for more air tanks and gear along the escape route to be replaced, a process that would take between 10 to 20 hours.

"Our job is not completely done," Mr Narongsak said on Sunday.

"We will have to do the next mission as successfully as the one we did today. The rest of the kids are in the same spot."

Mr Narongsak said that 10 cave divers had accompanied the boys throughout the journey, which took a shorter time than expected.

Officials had earlier said that the earliest time the first boy could get out would be 9pm local time on Sunday.

The first boy emerged at around 5.40pm, followed swiftly by the second at 5.50pm. The third and the fourth came out of the cave at 7.40pm and 7.50pm respectively.

"They hugged the boys beneath them while they were wearing full-face masks," Mr Narongsak told reporters at a press conference on Sunday night.

Ropes were put in place along the route to help the divers and the boys navigate a treacherous network of narrow and submerged passageways, which claimed the life of a former Thai Navy Seal diver last week.

There are several narrow "chokepoints" in the 10km long cave network.

Rescue officials have said that the biggest crisis spot is a 38cm wide crevice close to the T-junction, or Sam Yaek Junction.

Tech billionaire Elon Musk shared via his Twitter account photos and videos of a metallic capsule that may help rescue the boys. The tweet shows a group testing the device in a Los Angeles high school swimming pool.

He said in a tweet on Sunday (July 8) that the pod, which is described as a "kid-size submarine", was en route to Thailand and would arrive in about 17 hours.

"Hopefully useful," he said in one tweet. "If not, perhaps it will be in a future situation."