A total of eight boys have now been recovered from the flooded cave in northern Thailand, as rescue efforts concluded for a second day.

Operations are expected to resume again tomorrow to extract the final four boys and their 25-year-old coach who are still trapped in the Tham Luang Nang Non caves in Chiang Rai.

The world has been riveted as it has watched the fate of the 12 young footballers and their coach who have been trapped in the treacherous cave system from more than two weeks.

Heavy rains flooded the sprawling network of caverns and tight passages, cutting off their only route out.

Officials today confirmed that four boys are now "safe and conscious" in hospital after they were extracted in a complex rescue effort.

They joined four more who were removed on Sunday on the first day of the painstaking operation, which has also included help from elite British divers.

As the operation is expected to begin again tomorrow, Chiang Rai acting governor Narongsak Osatanakorn said he is not sure if the remaining five people in the caves will be extracted in one or more operations.

He said Thailand's prime minister Prayuth Chan-ocha, who visited the cave site yesterday, has gone to visit all eight boys in the hospital.

The Facebook page of the Thai Navy Seals, who have been central to the rescue operation, was updated this evening to say "two days, eight boars" - a reference to the Wild Boars, the name of the boys' football team.

"This morning they said they were hungry and wanted to eat khao pad grapao," Mr Narongsak said, referring to a Thai dish of meat fried with chili and basil and served over rice.

The four are undergoing medical checks in a hospital in the provincial capital and were not yet allowed close contact with relatives due to fear of infections. Relatives were able to see them through a glass partition, the governor said.

It has been a desperate effort to help extract the boys, whose ages range from 11 to 16, as the annual monsoon season approaches and is expected to flood the caverns in the mountainous region in far northern Chiang Rai province.

Workers have been labouring round the clock to pump water out of the cave, and authorities said heavy downpours overnight did not raise water levels inside.

Fear were also raised about the levels of oxygen in the caves, which were dropping dangerously low.

The risks were also underlined with the death on Friday of a former Thai navy Seal who was working as a volunteer in the rescue effort.

Sgt. Major Saman Gunan died on a mission to place air canisters along the passage to where the boys were, necessary for divers to safely travel the five- to six-hour route.

The boys and their coach went exploring in the massive Tham Luang Nang Non cave on June 23 after football practice, and were cut off when a rainstorm flooded the cave, sparking a massive 10 day search operation.